If you are looking for 36-39 Chev 1/2 ton fenders, they are hard to find. If you are just trying to find a good looking fender to bolt to the box, the Model A through 32 Ford fender looks nice mounted to the early Chev boxside.
Fiberglass are available,I have glass fenders and running boards on my 37 and no one can tell they are not steel.