I think you're stuck with fixing yours if you want the truck to come out OK. I also have a (C-1 in pieces).
I know of no other fender that would pass muster.
Keep in mind the C-1 is a gorgeous truck (even old Ford people agree) and that stock rear fenders are part of that gorgeous package.
I HAVE seen C-1 rear fenders for sale on Ebay and other places but the prices are astronomical.
If I had to come up with rear fenders here (in dry, antique-truck-full Central CA), I'd scout the "old pickup trailer conversion scene" until I found some. I can't afford $1500 for FENDERS. They are probably worth every penny, though.
One more thing...Chevies and Internationals of this age fell apart early because of all the wood in the cab. That means mid-30s IHC and Chevy pickup beds were made into trailers more than other makes once you account for total sales. These "conversions" often have the stock front axle, wheels, springs, too. A veritable treasure-trove.
BTW, I'm putting Model A fenders and pickup bed behind a 1934 Ford PU.
I have no room to talk. However, THIS 1934 Ford is a cut-down 1 1/2 ton truck.
All just my opinion! Best of luck!