I take it that you need what Fairphone’s Repair Service calls the “Rear Module”. If you’re not in a hurry, I could send you a used (but good condition) Rear Module next week. I might even have both the opaque black and the black translucent version, but I’ll have a look later.
Yes, it has never been available directly for purchase in the spare parts shop, only ever through a fully-fledged Repair ticket. I realized that only one of the rear modules that I could offer has a fingerprint sensor, so I’ll see which one it is.