Bluegrass might be challenging if only because of the fast tempos at those jams. Look for a beginners jam session. You probably only will be able to play along in the keys of G and C. Same information goes for country jams except that the tempos usually are more leisurely.

You might want to look for Old Time music sessions where the melodies and musical phrases tend to be simpler and usually are played over and over so that by the end of the tune you’ll have a pretty good idea of it.

Also, you’ll also want to look for an accordion in the key of D to be able to handle all the D, G and A tunes although in G and A you’ll be missing some of the notes.

Good luck and have fun!

I already play several instruments, including OK guitar and OK banjo (not great at all). A couple of years ago I got interested in the Cajun accordion. I ultimately purchased a C and a D. Played Cajun accordion as taught by the Savoy family at Fiddle Tunes here in the Seattle area, (Port Townsend), and later by Blake Miller with Cedric Watson.

So I play a few Cajun tunes now, and also sing in French (need to read the lyrics so far). But there is minimal opportunity for playing in a Cajun setting here, so I go to a weekly old time fiddle jam, where most of the tunes are bluegrass, Appalachian, some Tin Pan Alley tunes etc. I also go to a roots jam where it is mostly county blues.

Almost all of these tunes, I can accompany on either the C or the D accordion. Its fun, and for the most part, is received OK. Seems like you can accompany in quite a few keys adequately on the C and D boxes combined.