You can get 9R22.5" tires from any regular truck tire shop.
They are made by all the usual suspects.
For a rough tread, I think that Goodyear G124 is the most grippy looking of the choices available.

Grigg


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-