Off the top of my head, try these places. Rocky Mountain Euro Sport at 303-742-2222. The main guy there is Leon, he sells the majority of the cars. He'll know of a place to get work done on any BMW. His place is off of Leetsdale and Quebec, great shop for all sorts of cars.
If that doesn't work out, try calling Murray Motors and speak with Ben Uher, pronounced U - er. He'll have some suggestions, 303-759-3400.
And last, if both of those fall through, you can always try Jazz It Up. They work on all sorts of cars and if anything, might be able to recommend a good place. 303-799-8290. Hope this helps.