Why, oh why can't I get the train sites to work for Madrid-Toledo

Maybe you're still just a little too early? I can get the Renfe site to sell me a ticket for that route up until June 11th and then they don't seem to be for sale yet. If you play around on the website I think you'll see what I see.

The summer schedules are not loaded. Try tomorrow.

From the man in seat 61 website regarding train tickets within Spain:

"Spanish train bookings usually open 60 days ahead, although AVEs may open up to 90 days ahead. You can't book before reservations open!
If you see Train blocked in the search results it means that date or train hasn't opened for booking.
The opening of reservations can be delayed for dates after the twice-yearly timetable change in June and December, as they're always late loading the data.
The 60/90 days isn't exact, indeed, I often find that Renfe loads trains as and when it feels like it, often less than 60 days and sometimes certain trains appear on the system before others. If you don't see the complete train service which you are expecting to see, and it's over a month to go before departure, the chances are that not all trains have been loaded yet."

It's possible that they have not firmed up all timetable changes for June yet. You'll probably just have to keep checking until they are available.

Any suggestion of advance purchase being available in a whatever amount of days ahead is certainly no longer valid and has not been for a considerable time. Simply monitor RENFE's site on a daily basis.

Neil is right, there seems to be no hard rule anymore on when RENFE tickets become available online. 60-90 days is just a general guideline.

I wouldn't worry too much about getting the tickets in advance if you are not able to. Sometimes specific trains on that route do fill up, but it isn't a huge problem and there are numerous trains daily. You can also take the bus which doesn't take that much longer.

The biggest problem is waiting in line at Atocha. Lines can be very long and be sure to get in the line for "day of" or "travel today" ticketing. So arrive plenty early before the train you want or you might be on the next train anyway.

I'm sure they give more priority to confirming and loading longer, more expensive train routes into the system first. Especially with the June 12 schedule change, "lesser" routes can be delayed, as well as any route that has had construction or where they might be introducing a significant change (like a new leg of fast train). Everyone who wants that train is in the same boat.

I've also been trying to book tickets for mid-June (bar to mad). The AVE tix from Barcelona to Madrid were loaded less that 60 days in advance for mid-June. After checking daily, I was finally able to purchase tickets. Just keep checking. I think they may just be back-logged in loading the summer trains. You may want to check captaintrain.com - it has been super easy to use.

Thank you all for your very helpful responses!