While I didn’t get to attend any organ concerts while in Paris, I did manage to get over to Saint-Sulpice just before their solemn Mass for the Feast of Corpus Christi. Here is a short clip of some of the prelude music that was played. I stayed until the opening prayer; I wish I had had the time to stay for the whole thing and hear the postlude(s)! Not sure if this piece in the video was improvised or a composition.
Hopefully on a future trip to Paris I’ll be able to attend some recitals.