If you're looking for something like Dinan then there's Leith BMW in Raleigh, Fletcher BMW in Fletcher and Crown BMW in Greensboro.
If you looking for something a little more tailored to you then there's Korman Autoworks in Greensboro. They're good people. They used to work on my E36 M3 - back in the day. There also very big into the BMW community. Here's their link:
http://www.kormanfastbmw.com/index.html
I don't see any E90 items on their website, but I'm sure they'd be glad to work with you....
enjoy.....