Train Ticket advice

Try in another month. The tickets for train travel in France is only showing for purchase up to May 2020.
When you search your date of travel the site lets you sign up to alert you via email when your route is available for purchase
https://en.oui.sncf/en/

FYI: There is no train from Bordeaux to San Sebastian. The last stop in France is Hendiaye.

You need this site to go from the French Border town Hendiaye to San Sebastian Spain
https://www.euskotren.eus/en

San Sebastian to Madrid you buy on this site when available 30-60 days in advance
https://www.renfe.com/

Man in Seat 61 is very helpful for train travel. He has lots of tips and video on train stations and such. Exactly how to buy tickets with several ticket systems and which is best for each situation. Poke around and you can get everything (and more) that you need to know

This is Paris to Nice, Lyon, Bordeaux, etc
https://www.seat61.com/international-trains/trains-from-Paris.htm#Paris-Nice

Great advice! Thanks!

The fastest train routing from Bordeaux to Madrid will take 9 hr. 11 min., and it doesn't go anywhere near San Sebastian. I don't know how much longer it would take to go by way of San Sebastian; it would be somewhere north of 10 hours, possibly as much as 12 hours.

I'm not sure why you specified traveling by way of San Sebastian. You won't have any time to see the city unless you spend the night there.

Therefore, you might consider flying. There are 3 non-stop flights from Bordeaux to Madrid on June 25. The fares range from $43 to $57, according to Skyscanner.com. I haven't gone to the airline website to verify the fares. You should be able to find them listed on the Iberia website, but the flights are operated by "Canaryfly for Air Nostrum AS Iberia". No, I haven't heard of them, either (and I don't fly airlines like that, in truth). Checked-baggage fees will be extra, and there's likely to be a very low size/weight limit for your carry-on bags.

Do you really have to go to Bordeaux on this trip? If you must, you should start thinking now about how much time you want to allow between scheduled flight arrival time and train departure time. The Bordeaux-bound TGVs depart from Paris-Montparnasse Station, but there's an 8:11 AM train from CDG (no guarantees you'd make that). For the later trains you'd first need to get to Gare Montparnasse downtown (by train or some other form of transportation). You'll have to select a specific train when you buy your ticket. The cheapest tickets will be non refundable; I'm not clear on the rules about changes; I think they vary by ticket type. It appears the walk-up fare can go as high as 111 euros from Gare Montparnasse and 141 euros from CDG.

I did a bit of research and was able to learn that we can take a train from Bordeaux to Hendaye, approx. 2 1/2 hrs., and then transfer from Hendaye to San Sebastian, approx. 30 minute trip. We could either stay in San Sebastian for the night, and head to Madrid the next day, or take the 2:30 pm train that day, arriving in Madrid around 8:30 that evening, it's a 5 1/2 hr trip.
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Actually for French trains, bookings now open 120 days ahead instead of 90 on main TGV routes. So for Paris-Bordeaux, you can have a look on Sunday already.
But why Bordeaux? There's barely a day of sightseeing there, unless you do a lot of wine-related activities. I'd aim straight to San Sebastian, or Biarritz if you want to spend a few days on the French side.

We want to spend a couple days in Sarlat. I found the episode Rick taped in that area very interesting. I thought the smart (quickest) thing to do would be to take the train to Bordeaux, and rent a car there, and then drive to Sarlat.

Sarlat and its area are lovely, but travelling around these parts is painfully slow. You absolutely cannot do the region justice in basically one full day, recommended stay is at least 4-5 nights, not 2.
I strongly recommend heading straight to the Basque country, where you will have your fair share of quaint towns in verdant settings.

You're quite likely to be sleep-deprived and jetlagged when you arrive on June 23. It's an extremely bad idea to go to Bordeaux, rent a car, and spend probably at least 4 hours driving to Sarlat (plus time spent stopping for lunch). Are you sure you'll be safe to drive?? I would definitely not be. Then you'll arrive in Sarlat in the late afternoon, wanting nothing so much as to go to sleep. You probably won't have the time, the energy or the initiative to do much that day. So you'll really have basically one day (June 24) to see a tiny bit of the Dordogne, and you will have subjected yourselves to two utterly exhausting travel days to pull that off. The Dordogne is a wonderful area, but it's not a good place to spend one day if you have to kill yourselves to pull it off.

The next day (June 25), you have to allow time to drive back to Bordeaux (4+ hours) and return the car (possibly not exactly instantaneous) before getting on the train heading to the border. There are Bordeaux-Hendaye trains departing at 7:42 AM, 10:02 AM, 12:02 PM (arrives 2:31 PM), 12:50 PM (arrives 3:21 PM), 2:50 PM, and 3:02 PM. What time will you need to step into the car in Sarlat to be reasonably sure of making the 12:02 PM train--6:30 AM? You may still be jetlagged on the morning of Day 2. I would be miserable and not necessarily safe to drive.

So let's say you do make that 12:02 PM train out of Bordeaux and arrive in Hendaye at 2:31 PM. If there were a 2:30 PM San-Sebastian-Madrid train on the Thursday schedule, you'd miss it, but I don't see one. It looks as if your departure-time choices from San Sebastian will be 7:28 AM, 8:57 AM, 11:14 AM, 2:04 PM, 4:10 PM and 4:33 PM.

It's about 16 miles from Hendaye to the San Sebastian train station; I don't know what the drive is like or how long it's likely to take--or whether it will be difficult to get a taxi in Hendaye that can/will take you to San Sebastian. But the best you can hope for is the 4:10 PM train, which will get you to Madrid at 10 PM, at which point you will have been on the move for 15+ hours. (The good news is that shooting for the 4:10 out of San Sebastian means you might feel comfortable taking the 12:50 PM departure from Bordeaux and sleeping a few minutes longer. I wouldn't, because stuff happens.)

Trains do not always run on time. That's probably a bigger risk with TERs (the 12:50 PM departure from Bordeaux) than TGVs (the 12:02 PM departure). Since the Bordeaux-Hendaye train is French, you have that annoying Hendaye-San Sebastian transfer to deal with, and the San Sebastian-Madrid train is Spanish, I'm not sure there is any way you can buy your train tickets and be protected so that the second ticket can be adjusted if the first train makes you late. I fear that if something goes wrong, you'll have to buy a new ticket from San Sebastian to Madrid. The full fare on the 2:10 train seems to be 72 euros.

One other thing: I believe French rental-car agencies often close for lunch. Be sure the ones you plan to use for pick up and drop off will be open when you need them.

This is why I love this forum! It def. helped me on our last trip to Europe, with all the fantastic advice. I'm definately going to re-think my itinerary!
Thanks, everyone. I'll probably be back for more advice!

Thanks to all for the great advice. So, here's what we decided to do:
-Arrive at CDG @ 6 am on 6/23
-Either shuttle, taxi or train to Orly to catch a 2:15 pm flight to Madrid
We are scrapping the Bordeaux/Sarlat idea. Next time.
Now my question is, does this sound like enough time to safely catch that 2:15 pm flight out of Orly? I feel that even with a delay, customs, and travel time, 8 hours is surely safe.
Also, of the choices of bus, train or taxi, what would be the best way to get there? We will get to the airport and more than likely crash, but I don't mind napping at the departure gate. I've done it plenty of times. Who knows? We may even get a bit of a 2nd wind and decide to spend an hour or so in the city. A light meal and a bit of time to absorb a little bit of the city might be nice. We have 2 1/2 days in Paris at the end of our 17 day trip.

Lisa, if you don't get answers here, post a new thread with a title like "How to Self-Transfer from CDG to Orly?" That should attract the attention of the folks familiar with getting to and from both airports.

I certainly think your proposed plan allows enough time under normal and nearly all abnormal circumstances. If your transatlantic flights is canceled and you can't travel until a day later, it will fall apart, but it's very difficult to avoid all negative impacts of that type of scenario.

I'll do just that. Thanks for all your valuable advice!