I used to know a parts man at my local Chevy dealer and would buy whatever trim items were available (this was the late 80's) for 66-67 Chevelles. The hardest part was getting the parts guy to spend his time looking and ordering. I was surprised at what was still available back then. These were some of the same parts the aftermarket guys were selling. The buying public just didn't know they were available. I'm not looking now, but, just curious if there are any parts still available. I bet there has to be a few hard items for the underside of the car, but I'm wondering about any trim items.

http://www.gmpartsdirect.com/restoration_parts/index.cfm

look here. I have used the GM part numbers and have bought a couple of items

GM has been getting rid of parts and warehouses because they are broke, even parts for current model cars (early 2000s) are being discontinued. They do sell replacement parts and reman but not items that match OEM.

Classic Muscle
Division of Modern Chevrolet
5415 Kelley-Moore Drive
Winston Salem, NC 27105
(800) 722-4828
(336) 727-4828
FAX (336) 727-4846
www.1964-77chevelleparts.com
They have some repro stuff but a lot of NOS stuff too.