I know of a few places that sell AC Schnitzer parts (but I'm sure there's more if you search around on google):
http://www.hmsmotorsport.com/store.php?b=acs
http://www.vividracing.com/catalog/
http://www.cecwheels.com/
Their websites might not have Schnitzer stuff available for the E90 yet but maybe you can e-mail ahead to find out availability/prices, etc...