Cool Music Instruments’ Chromaticover is slightly bizarre device that turns your synthesizer into an accordion.
The Chromaticover is a hardware chromatic keyboard, with an accordion-style mechanism for both right hand and left hand. The keyboard features magnetic MIDI sensors, with the key touch of a real accordion.
The Chromaticover sits directly on top of your existing keyboard or piano keys so you don’t loose any additional space. It has been designed to fit any keyboard: it just sits on top of the existing keys, making your instrument a fully operational chromatic keyboard.
Left hand: 120 active bass buttons
Right hand: 86 active buttons
Details at the Cool Music Instruments site.