I bought a large sheet of 1/8 inch free machining brass years ago for my gears before brass became the price of gold. Some of the older cirkuts use gears that are made from thicker brass and I scrounged a piece of 3/16" for those. I was going to make a gear out of a fifty cent piece once just for a joke. It would probably work.
Some of the commercial places that make gears seem to make "thick" gears and they really don't mesh well with the cirkuts. They are advertised as 32 pitch, 14.5 degree pressure angle, but the fit to the original ring gear is lousy. That is why I started making my own and taking a close look at the original gears and their fit.
The ring gears are made from one piece of flat brass, not a formed strip. And yes you can use them without the plating as most of the old cameras seem to have worn plating. I've even seen deep ruts, but that cannot be good. A simple fix would be to make a thin flat ring slightly smaller than the gear teeth that fits on the top of the gear and just glue it down if nothing else. A guy could use thin stainless and it wouldn't increase the height enough that the pinion shafts would be affected.
Although I have blanks cut to make 12" ring gears, I've never made them because there has never been a demand and I have enough for my machines. Mostly the issue is my lathe cannot swing that diameter and I need to us a friend's. That makes for a lot of running around. I've always wanted to make a ring gear with an odd number of teeth to change the ratios for some of the different lenses I use. A 10 inch ring gear would be better for wide angle work and a 14 inch gear for telephoto stuff would be dandy as the pinion gears would be slightly bigger.