Re: Aurevoir Grand Mamou by Steve Riley on accordian
The song is definitely in the key of G. In the chord progression, in addition to G, C and D chords, there is also E minor.
I haven't tried it myself yet, but I agree that it is likely that Steve is using a C accordion in the song. My first reaction is that I don't hear anything that leads to me to think that he's using a modified C accordion with extra buttons. But I need to give it a closer look.