I get asked every so often to help do just what your asking, so here is my process. I start with the local sources. Craigslist, Traderonline, Cars.com, and local newspaper classifieds. Then move on to to things like ebay. What your looking for isn't exactly common in the states but they are out there so it may take a bit of time and searching. When you do find one then its just a matter of what you would do with any used car. Check it out, test drive it and it's most likely more than worth paying good beemer shop for an hour of their time to give it a good going over if you're not confident doing it yourself or just want a second set of eyes on it. Good luck and good hunting. Let us know how it turns out.