You are looking for 22.5" x 6.75" wide 6-lug tubeless Budd Wheels. As Mike said they are out there and not that hard to find.
The tubeless tires are always one size larger numerically then the matching 20" tires, so a 8.25 x 20 will be the same width and diameter as a 9.00 x 22.5 tire and a 9.00 x 20 matches up to a 10.00 x 22.5.
The Firestone RH-5's were discontinued decades ago due to them being unsafe and having the capacity to explode apart without warning. They can be ID'ed by the 2" locking band running around the center of the rim, there is no lock ring at the tire bead. If this is what you have
DO NOT AIR THEM UP IF THEY ARE FLAT as they force they generate when they blow apart can lift a car off the ground...your head and arm don't stand a chance!
Mike B
