There is a magazine called trad at

http://www.tradmagazine.com

Each issue has a calendar of over 1000 folk dates all over France. I don't think the calendar is available online, but you may be able to email them and find out where the magazine is sold in the first town you visit.

The most active Traditional Music associations are in Brittany, (La Boueze and Dastum in Rennes) but the AMTA (Agence de Musique Traditionnelle d'Auvergne) in Riom or Vie et Tradition en Normandie in Avignon may have information on other parts of the country. I don't have phone numbers, I'm afraid!

There is also a folk arts museum which you should visit in Paris:

Musee National des Arts et Traditions Populaires
6, av. du Mahatma Gandhi, 75116 Paris
44 17 60 00
44 17 60 60

(The Les Sablons metro station.)

They have a sound archive, and someone there may have information about where you can hear traditional music while in Paris. Certainly they can point you to the regional research centers in the areas you'll be visiting, who in turn will know about any events during your stay.

Keep in mind, in addition to "folklorique," the French use the terms "Musique Traditionelle" and, more generally, "Arts et Traditions Populaires." Ask concierges, tourist information people, etc., about these areas.

best of luck!