I've collected a couple sets and seen others on trucks at shows and occasionally on a truck on eBay or Craigslist.
I'm sure they're out there if you keep after them.

I've only ever found them at 5.25" wide.

One set I have with bad rims I'd like to use the centers on a 6" rim, then they'd fit a 9R22.5 tire by the book.

•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-