As
@Kathar1na helpfully explained in
this thread, the train route from Bayonne to SJPP has currently been replaced for a segment of the journey by a connecting bus from Cambos-les-Bains, and it seems that all future searches for that itinerary include the connecting bus (even though an official SNCF notice shared by
@JabbaPapa in
this post indicated the bus connection replacement was only in effect until the end of February.) It seems it's for track repair/maintenance so perhaps the train will return at some point in the spring, but for now all searches through mid-May include the bus in the itinerary.
I was able to buy a Paris to SJPP ticket for May 6 via the SNCF website a few days ago, so booking is definitely now open through at least that date. I just tried searching for April 14th for you and came up with the following:
View attachment 118003
It seems the SNCF website is very sensitive to the time of day you search for in your intinerary, in addition to the date - and when you search, it will autopopulate that search field with the local time in France. So if you're searching, say, during the day here in North America or in the evening in Europe the search results might come up nil since there are no trains leaving Paris after mid-afternoon. Try searching again with an early morning time (say 09:00h) and see what happens.