"You sometimes can find GM5 modules on ebay or by specialist breakers but you will have to have the unit programmed .
Scott, of the BMWGM5 website, can do a service for a very reasonable price. Or you can order the parts (relays) from him and do it yourself. There is plenty info available of how to do it.
I have just noticed this thread, I got 2 new relays last year & fitted them myself, carefully, but using an old soldering iron & great care while sat in the Kitchen late at night when i wasn't going to be disturbed! I used some solder extractor, which you put on the soldered joint & this draws the old solder out when you heat it up. Some of the finer connections where difficult to draw out, but i found it was easy if you first added some solder which then gives you a bigger blob to work with when trying to withdraw the solder. The removing of the solder is the hardest bit, re-fitting the new relay is the easy bit.
I would say be brave & give it a go, too many people give up too soon or they have too much money!!! " - Quoted from another source.
Hopefully that helps (I couldn't be bothered to read the whole thing).