I have a couple of motorized Mamiya RB67-Pro-S 120/220 backs (used but like new and still boxed), but I'm not 100% sure about compatibility with your camera. They actually was spare backs for a film-recorder machine based on that Mamiya camera. Maybe some expert can advise about them...

Here's some pics:







This was one, the other one is exactly the same. Let me know if you are interested. Bye