A couple of places:

Precision International (Sardis Road, near Biltmore Square Mall). Mark knows BWMs well. They also do Saab, Volvo, etc.
23 Sardis Rd
Asheville, NC 28806
(828) 670-9191

Joyner BMW Specialists - Chris and John know their stuff and are great guys. They're booked until infinity it seems. Both are involved in the local BMWCCA chapter.
76 S Market St
Asheville, NC 28801
(828) 253-6000