Back of my key fob cracked while replacing the battery. Is there a decent place to get a new one without needing to replace the entire key?

Just trying to find the back cover part that says MINI.

 

I doubt you can buy just that part alone. Probably best to look on EBAY for something that will cover it after you put something over the battery with duct tape or simiar. You can probably find a cheap full EBAY special and transfer the guts into a new case.

 

Not from the dealer the entire fob only, like Minnie the moocher mentioned maybe find one on eBay just to get the cover

 

Pricey but cool looking and an exact fit https://funfob.com/