Most tire shops can find tires it you are not too picky about wanting them fo look exactly like original 50s tires. If not try Coker tires they look old And I've had good luck with them except for some of the whitewalls.
I happen to like the looks of "split" rims on a truck. They have some disadvantages for models use.
1. You'll have to run tubes & probably flap between the tube & rim.
2. Many shops won't mess with them or will charge extra.
3. If you don't know what you are doing and don't have the right tools they can kill you.
I worked in a tire shop when I was going to JC after high school. They found out I could do them so I got them all. Some I refused to do but if they were in reasonably good shape I'd do them, but I took my time and would not babe rushed. We didn't have a cage so I inflated them using s couple of short chains and set them under one of the car lifts. Never had one come apart but ai saw a terrible "accident" at a shop where my dad worked. One guy was killed and the other probably ended up loosing and arm. My dad had refused to work on their old rusty wheel so they left and came back later and without permission they tried to use air pressure to get a ring loose. They did.
I ran them on my '40 International 2 ton. 20" six of them that required that I take apart 12 to get useable tires and a set of wheels that matched. I had them sand blasted and then I painted them. Did it all in my driveway with hand tools. I wouldn't do it again but I see the truck at Hot August Nights and they are still on it 30+ years later. I also had them on my '53 for a while. Those rims are still around.
I just went out to check a '50 GMC 3/4 ton in the yard. It has 4 different 16" 8 lug wheels on it. One is a split.
Your truck could have come with either 16" or 17" wheels. 16s might be easier to find but 17s are popular again now too. I'd look around for a nice set that are right for the truck and that fit modern tubeless tires. I don't like modern looking wheels on our old trucks with only a few exceptions.
Also if you are going to rebuild a six build a GMC!
