via this Vemia listing
Click the auction link on top when you get there for additional listings.
"These are 12 (the full keyboard extension) extremely rare chips, perfect replacements for the unobtanium MM5823N built by NATIONAL SEMICONDUCTOR. The original ones do break after some years, these are made with new electronic components, so will last a life... Remember, if you have one of the following, you need them: these Ics are brand new ones, and are used on different types of synthesizers (Hammond X5,Korg PE-1000,PE-2000,PS-3100,PS-3200, PS-3300). I bought them for future maintenance of my PS 3200. Now it's gone."
