My guess is if they had been silvered they were probably "orginals" NOS or NORS. The repros you get now are chrome plated.
Have a look at Marco's site.
http://abarnyard.com/workshop/lamp_focus-2.htm to see the difference between the originals and the repops.
The part number for the gaskets at Brattons is:
Part #18120.
HEADLIGHT LENS GASKET
For Year(s): 28-34
Rubberized CORK.
Part #18120 HEADLIGHT LENS GASKET $ 3.25