Writing an arrangement or a sheet music for accordion has its own peculiarities, especially when dealing with the left hand (bass). If you are a music enthusiast, engraving your piece in Lilypond, a free and open-source music notation software, is advantageous for various reasons. Lilypond not only delivers great printouts, but also allows producing MIDI files. I have created a github repository, which you can use as a starting point for typesetting your own accordion music:
A simple example is “Jingle Bells” by James Lord Pierpont: sheet music.
Work-in-progress is an arrangement for accordion of Vivaldi’s RV 93 : sheet music