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I would say that the more modern 19.5 and 22.5 would have more options/availability, but even the proper 8R19.5 or 9R22.5 is considered scare by some. Fortunately, most circumstances allow for use of the 225/70R19.5 or 235/80R22.5 instead respectively.
Proper answer, there are no both easy and cheap options that are safe for public roads.
You have to go to 19.5s or 22.5s and the tires cost more than most of us pay for our trucks here.
If I were you I would look for some 22.5s for it as they are a near match to the original tire size.
Or you can get some adapters and put 10 lug super singles on it.
On the bright side the tires last forever tread wise.
These adapters are not currently manufactured for market and deemed likely much more costly than finding traditional buds style rims when getting custom manufactured. Also, these adapters likely will have steering/clearance issues on the front axle. An interesting idea, but not yet fully flushed out or available.