In a related topic - for the ANGLO concertina, my program HARMONY can produce tablature from various inputs, including abc. This may be of help in accompaniment.

It can show you, by various means

1. Which notes CANNOT be played - often happens!
2. Which notes can be played in either bellows direction
3. Runs playable without changing the bellows direction, across rows
4. Chords

To find a chord, all you have to do is make up a short abc file containing the chord notes in each octave, IN SEQUENCE, such as 'ACEace' for Am chord, or even A,C,E, A C E a c e a' c' e'

It will then show which buttons can be used for that chord, on the tablature.

http://www.greenhedges.com