Planning train travel from Paris to Lyon in early October - the only option from SNCF is a 'regional train' - not high speed.
Am I looking at the wrong site?
It is too early to book tickets and the SNCF site is primarily a ticket shopping cart. To simply see train schedules, How to Look Up Train Schedules and Routes Online gives you the DB train schedule link and tips for using it.
Yes, wait until 3 months before the day you want to travel and the TGV's will go on sale. That would make it early July.
As a suggestion for booking French and German trains I offer that you look into Capitaine Trains which is a relatively new train booking site for these countries. No fees for booking are charged, plus you can make seat selections!!! Once logged to the site you can select you trip. If is is not available for ticketing now (for Oct it is not), you can request a notification email to alert you when available. A Google search will quickly bring up the website and a free app can be downloaded to an iPad or similar device. We have traveled from Lyon to Paris on a TGV and I would assume that possibility still exists. I have not confirmed that but Lyon has two major trains stations Gare Perrache and Gare St. Exuprev TGV. Note the last has "TGV". I also suggest downloading the app for Gare360 which is an excellent website for literally walking through French train stations in 360 degree videos so you can easily transit to platforms, ticketing areas, locating "yellow boxes" and taxi stands.
THE main train station in Lyon is Gare Part Dieu. St Exupery is the airport 10 miles outside of town. You definitely don't want that one. There will be a TGV every hour from Gare de Lyon in Paris that will get you to Lyon's main station (Part Dieu) in 2 hours or less. Just wait till they go on sale.
Lyon has two major rail stations:
Part-Dieu: in the eastern part of the central area and served by TGV trains. Linked to the centre proper by Metro, tram, or bus depending on what exact location you want to get to.
Perrache: the "old" station, with a more central location but served by local trains and Paris Lyon TGVs which end at Lyon and don't go further south.
The two are linked directly by tram route 1. Lyon has a good public transport system, but you do need to check how to get from the rail station to your hotel in advance, as the range of choices and routes can be initially overwhelming.