See
http://lapaixdemenage.fr/Says there is a week looking at improvisation w/c 1st July. Followed by accordeon w/c 7 August. There are also clarinet and song modules going on, making it possibly a pleasant week (or two)for some couples, or pals. Not been to this particular venue myself, but they rarely disappoint. The leaflet says it's 3000ft up, so cool. And "don't trust your satnav"!
You'd benefit from a 2½ row for their improvisation week, though IME a DG# is just fine. The accordeon week is likely to be tunes for which a GC is much preferred. Stef Milleret leading on box
There is also mustradem.com famous (25
th year!)
musique traditionelle course 14-20 August (was in Isère last year) which covers most instruments, and song. The accordéon section has beginner and advancer groups (GC preferred) doing mainly melodies and technique. Group III do improvisation … so 'flexible' as above.