Yes, unfortunately it seems to be a very, very long shot to have this chip replaced...
I'm curious if it might be a possibility to reverse engineer the IM368/R6500-1 by logging the i/o communication across the pins somehow and using AI to piece together the code for the correct environment with another programmable microcontroller? Perhaps AI aided coding is up to the task?
Reverse engineering is a fools errand. The IC was made by Rockwell. A Rockwell R6500/1EAC with some customizations.
But if you wanna buy a replacement, we have several on hand:
https://shop.synthesizer.repair/product/emu-im386-keyscan-ic