Most shops won't let customers bring in part b/c the 'warranty' on the work can't / won't be offered with customer-sourced parts. The truth is that they make a profit on the parts (this is normal).

This warranty excuse is generally BS especially if you're buying / using OEM parts. Bavarian Autohaus in NH is a reputable BMW parts source.

Brakes and rotor replacement is one of the easier DIY repairs. If you don't wanna do it or lack the tools, a local shop can put them in for you.

I would avoid the chain shops (Midas, Jiffy Lube) and use a local mechanic (i.e. the shell station) someone who you trust. You don't need a BMW specialist to do this kind of work.

GL