Hello,
Do you have Jean Pierre Gregoire's birth date and birth place, as a place to start? With this it might be possible to find the birth record for him, which might tell where Pierre Gregoire is from.
I think Lyon is in the department of Rhone (69).
These websites might be some help to you. You might already know of them, if not I hope they will be some help to you.
http://archives.rhone.fr/http://french-genealogy.typepad.com/Good luck in your research.