I would try Martin's Import Salvage in Wendell- or call Jeremy at Wagner's, even if they don't have what you need in stock, the old school junkyards get stuff from other yards all the time.
Or Ebay, seriously- you'll likely have to weed through a ton of JDM style new aftermarket crap headlight listings, but you should be able to find what you need at a decent price if you poke around enough (and use some search filters)
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EDIT: $63 with free shipping and you're back in business at least temporarily-
http://www.ebay.com/itm/2008-2009-2010- ... TP&vxp=mtrhttp://www.ebay.com/itm/2008-2012-BMW-3 ... gX&vxp=mtrhttp://www.ebay.com/itm/2008-2012-BMW-3 ... CG&vxp=mtrhttp://www.ebay.com/itm/2008-2012-BMW-3 ... 4y&vxp=mtr