Want to Buy WTB: Mamiya RB67 film back

Looking for a RB67 film back for a 3D printed camera project. Looking for either Pro or Pro S, but not Pro SD. Let me know what you might have. Thanks!

Why not ProSD?

Also worth noting that most likely any 2x3 Graflok mount roll back will work (I have a Graflex 22 that works fine on my RB67, for instance). It probably doesn't have to be RB67 specific.