I discovered a new instrument today ! This is a Hohner Electronium which at first glance looks like a normal electric accordion. However the electronics are actually a valve driven monophonic (meaning only one note can play at time) instrument. This makes it close to being the accordion equivalent of a Clavioline. Interestingly it was designed by René Seybold who also made player accordions.
This particular specimen is currently on Ebay in Germany however from the approximate translation it seems that the amplifier is missing.
Link: Electronium Ebay Auction
Link: More pictures and information about Electroniums can be found here (click on Tasteninstrumente)