The originals were plastic (I might make a small run when I get my new mill later this year). I made mine for the race car out of some .060 aluminum sheetmetal. Worked out pretty good.
I could also not find any source for them.
67 Coronet 500 9.610 @ 139.20 mph
67 Coronet 500 (street car) 13.300 @ 101.75 mph
69 GTX (clone) - build in progress......