You're pretty much restricted to BMW dealers for new OEM type parts .
May want to check around the SF area and see if you have any airhead friendly dealers there .
There's always eBay, but you don't know what you're going to get sometimes .
Online, A&S BMW in Roseville, CA., just outside of Sacramento is a popular site .
Bob's BMW, Capitol Cycle in the Washington D. C. area .
MAX BMW, somewhere in the northeast US .