Ben Gottfried asked for MIDI files for an Alan Pell 22-note accordion.
In an earlier response I suggested that it probably can play most
20-note MIDI files, omitting the bass. In addition to the 20er MIDI
files used for small crank organs, it should also play files used on
the Firma Watterott wireless organs, concertinas, and accessories.
Several 20 note scales are subsets of the Watterott scale.

I'm not sure how you can obtain legal copies of these files. They are
stored on SD cards supplied with the instruments at no additional cost.
There is a huge library (hundreds of tunes) in circulation. Both the
20-note and 40-note arrangements should play, but of course sounding
only 22 notes. For a description of the Watterott product lines see
https://www.ziehorgel.de/produkte?lang=en  The individual instrument
scales are at https://www.ziehorgel.de/dl.php?file=toene.pdf 

Rob Barker worked in the Alan Pell shop for many years. I think there
is a high probability that Rob actually worked on the instrument Ben is
concerned with, so I would suggest that Rob should be the go-to source
if more detailed information is needed.

Rob is currently offering a variety of models of what he calls an
Accordomotion which are, I think, extended versions of the 22-note
model. On his website he says air is supplied by an electric blower,
and an SD MIDI controller sends the music signals to hidden solenoids
under the keys to move them up and down. He says "A 48-bass accordion
will comfortably play 4-octave chromatic arrangements, whereas a 96-
or 120-bass accordion will handle almost anything."

https://robbarkerorgans.co.uk/ 

With regard to the instrument Ben is dealing with, we would have
a better understanding of his needs if we knew more about the MIDI
interface. I would guess that it has an SD card reader.

What is needed for any arranging is knowledge of the Channel(s) and
MIDI Note Numbers on the driver board. These could be worked out
experimentally, most easily if there is an actual MIDI port which can
be connected to a PC. Alternatively, arrangements could be tried via
the SD port or other input device. My guess is that they are MIDI
Type 0 files on Channel 1, just like the small organs.

Wallace Venable