don't know if this will help but there is a ring company in NY called niagra ring company and i
had some made for a single cylinder marine engine with a 4 inch bore and . 400 wide and
they were very helpfull.
I used Otto Gas Engine Works for my Fairbanks -Morse Z 15 hp. The original rings were 1/2 inch wide so I doubled them up and used pairs of 1/4 inch rings.
It was entirely satisfactory. They make rings from 5/8 inch to 86 inches in diameter so might be worth looking into.