Ben Gottfried asked for MIDI files for an Alan Pell accordion playing
a scale D,D#,E,F,F#,G,G#,A,A#,B,C,C#,D,D#,E,F,F#,G,G#,A,B,C.

This scale is essentially chromatic. Since note letters, not MIDI
numbers, are given, I can't precisely say where the scale begins,
but I would guess that it fully covers the Melody and Accompaniment
portions of the standard Carl Frei 20-note scale. In that case, it
should play almost and 20-er MIDI file, leaving off the bass.

It should be a good accordion add-on for many larger organs, if the
wiring is connected properly, and an accordion "stop" is added to the
MIDI files. It might be added as a Counter Melody if the driver board
is configured to a new Channel.

Ben said, "It is kind of an odd thing that Alan Pell made for my
customer." It may have been custom made for the owner, but Alan Pell
Organs accordions appear on Melvyn Wright's Organs for Sale listings,
so it is probably not unique.
Ref. http://www.melright.com/busker/adverts.htm 

Melvyn Wright can almost certainly provide MIDI files for it, as well
as Rob Barker. Ref. https://robbarkerorgans.co.uk/ 

Wallace Venable