I always check if Worldpac has stuff available. For example, I'd check here:
http://parts.autopartsonlinecanada.com/parts/apocanada/parts.jsp?year=1977&make=PO&model=911--004
If the parts are available there, that means just about anybody can get them (too bad they don't have a cross reference system for Porsche part no's though), then I get Concept-1 to order the parts in for me. Usually is a few bucks more than the online place, but they don't charge shipping, and it's usually quick.