You can get new Maxxis MA-1 from Coker Tire ( also via several places on E-bay). About the only whitewall I've found for quite some time. Kind of pricey but that's what happens when they become an oddball.....
A good friend who used to be into old Mopars but quit in favor of old tractors uses All stae Tractor 877-530-4430 or YesterdaysTractors.com for his go to parts suppliers.
Man, that old pickup is in great shape! Even has a decent tailgate. Those are usually beat to snot or competely missing. That would sure be an easy restoration or probably even a winner in a survivor class.