check out the parts catalog at http://www.bmwmobiletradition-online.com/bmw/
(or access it via www.bimmer.com)
At first it appears that you can only look up pre-e28 parts, but type in the last 7 digits of a modern VIN, and presto, the other half of the database is active. I haven’t checked to see if the prices are very competitive or not.
cheers,
bruce