Hot on the heels of the last one, another Chroniques of the BnF just arrived. (We're still not caught up, best to find the most recent online.) In it, I find an article reminding me that researchers looking for French manuscript collections have new ways of finding them.
The Archives et manuscrits catalog of the BnF is now available online, bringing together entries that were formerly only available in print. It contains records for manuscript items in the Manuscripts department, the department "Arts et spectacles," and at the Arsenal collections.
The other resources are within the CCFr (Catalogue collectif de France), the French "WorldCat" and there you can discover materials in municipal and specialized libraries and archives.
Within the CCFr, you can find the Catalogue général des manuscrits, or CGM- formerly the voluminous series Catalogue général des manuscrits des bibliothèques publiques de France.
And there you will also find PALME, the Repertoire des manuscrits litteraires francais du XXe siecle.
Search these separately or together (Manuscrits) before going on your research trip. Entries are also in the larger CCFr, but it would be more efficient to use the smaller catalogs.