Apologies for the slow reply! I haven’t actually done much biking that far over, but your first port of call should however be the FFC to find local VTT centres, these are a bunch of graded and signposted biking trails. Usually they’re pretty good place to start, and (vague) maps for the trails may be found at the local Tourist office. Failing that I’d just hit a GR (follow and red and white painted stripes you see on telephone poles, walls…) however that can be more adventurous than getting the local IGN Top25 map and just looking for interesting trails (the long distance GR paths are marked). Many Maries also waypost local walking paths (with yellow painted markings) that are good for biking.

I actually wrote a general intro to biking the area many eons ago, but it was lost in annals of CompuServe.

As an addendum, if you’ve never biked in FRance before, you won’t be disappointed. It’s a great country and biking is popular but you have to be prepared some gnarly terrain at times.