I wouldn't say they are that rare, at least not here in CA. I've seen a few, and about four in wrecking yards.
As far as "rare' goes...almost all of these trucks have been molested in some way shape or form, and even
the most pure restored truck will only fetch what you're willing to pay for it...some prices are outlandish, and
nobody will pay for the labor of the restoration. I'd love to find a sweet uni-body...

My advice is the same as Bill W's...if you like it, and it's solid...buy it and enjoy it...drive it.