This is beyond a shot in the dark … the discrete switch keyboard for the AIM 65 is one of the few keyboards that uses “sealed linear” Futaba switches. This is the one last series where the series designator (not necessarily the name) is still unknown. Things it won’t be are MA, MD, ML and MR, as these are the types with known part numbers or subseries. It is going to be M-something though, in a pattern like MD-4PCS or ML-3-CM..

I can’t seem to find a parts list for the AIM 65 that gives the manufacturer part number for the switches in the Futaba keyboard.

I don’t suppose this exists anywhere, does it?

(This is the rarest of the Futaba keyboard switch series apart from the reed type (AKA GRI KBR) which has never been seen at all. It shows up in the odd TI-99/4A too and other rare places.)