I ened up at my local Discount Tire. The Manager at the branch I go to is very knowledgable about Porsches and BMWs and knew exactly what I needed. They were even nice about mounting my tires which I purchased from TireRack. You could try calling "Jerry" who is the Manager and I'm sure he'd give you a part #.
Discount Tire (858) 279-4781
Good Luck!
