You can actually buy any similar BMW key fob and code it to open and lock your doors.
It cannot be coded to start your car.

So, some people buy used fobs on EBay, usually OEM, cut the key off, and attach it to their key ring as a open/lock fob only…

The problem is, how to charge the new fob on the key ring? it is not close enough to the ignition switch to get inductive charging.

Some folks have good luck charging fobs on certain tootbrush chargers..

Please have a search on this.