There were actually two "retro fit" midi systems that did just what
@Ben-jammin described.
One was a little silver box from Asimov Electronics (out of business) called UM83X
the other was a bigger box from Logic System (disappeared/assumed out of business) with a EK200 label. When looking for this one make sure it is for the proper accordion as it has a chip that is unique to the H or 83 but was used for others as well (petosa and others).
So essentially there were 3 ways to midi an H or 83 series. One issue is that the MIDI in the generator was a later addition and had to be special ordered, so not many of the original generators have them.