Hi

If it werte me i would maybe try to take the key off and sand the edge down a bit. If you don't fancy doing that take it to a instrument maker or accordion mender and they will sort it.

As for diatonic accordions having keys I have heard of a systm used on chromatic accordions which have squareish key like buttons! I can't remember the name of the systm of hand.

Hope that helps

Cheers, Sam