I'm not familiar with parts availability and part numbers for the older trucks but I wouldn't be surprised if they're available new. It sure wouldn't hurt to investigate.
I've had good luck getting brake parts at NAPA for things I didn't really expect them to have but they still did..

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-