Check a local tire shop. Years ago a local shop was able to get me Columbia branded tires for my 38. I don't know if that company is still making tires or not. When those wore out I bought Cokers. The Cokers are wearing better but took a ton of weights to get balanced. The picture below shows one side of one wheel. The frustrating thing was it had a like amount of weight on the inside of the wheel but 180 deg. across the wheel. I had them road force balanced. The problem with buying tires is there's little demand so each tire costs more to make.

I don't understand how they cost more to make under the laws of economics, I do understand they would sell slower, but material and labor costs are not affected by demand. It takes no more labor or materials than making a new tire. Coker has already recouped the mold costs decades ago. I think they hold a monopoly on old tires and shake us down on each sale now.

It costs $X to set up a run. If you run 1000 widgets each widget has 1/1000 of that cost in each. If you run 10 widgets you have 100 times more set up cost per widget. Also raw materials generally cost less per unit of measurement if purchased in bulk. Buying less material for a smaller run means higher material cost per unit as well. Lower production per run equals more cost per item.

These are not perishable widgets. If you sell 100 widgets a year and you make a run that lasts 5 years then the cost would be for 500 widgets and not 100 widgets thus you could purchase raw materials at a bulk price and not have to sell 100 then make 100, then sell 100 then make 100, then 100 then sell 100 make 100, then sell a 100 and make 100. You could make 500 in one run and sell them for the next 5 years. Thus production costs would significantly be cut due to not having to tool up and down 5 times and hedging that costs for materials and labor won't rise over the next 5 years by making them now not in the future as prices rise.

The actual costs can be very complicated to compute and understand. A couple of expenses you are ignoring are the time value of money and warehousing or storage space costs. Deterioration on storage, inadvertent damage and changing market needs also need to be considered. Ask the buggy whip makers if you can find one. Then there the alternate production options, (what else could you make with the time and raw materials) etc. And government actions that can make stuff worthless. Even professional accountants can have problems understanding the economic nuances. So what does that mean for those of us old car owners? Plenty! Do you want to buy fresh tires or a set that sat on the shelf 5 or 10 or 20 years deteriorating on the shelf? if you delay the purchase will the parts you need are no longer available. I have made that error way to many times. If you need or want them and can afford them my advise is to buy them and put them to use soon.

Chip.....nice to hear from you again. I have added 5 more Chevrolets to my collection and will be needing help on cars from 1927 to 1941. I  have always gotten good info here and will need it more now.