Hi Richard,
I had a lot of steering play in My All Cars Charley/ Snuggy due to wear on a big steering sprocket where it mounts to a steering shaft.
The elliptical indentures for accommodating the chain appeared to be in good shape though.
No matter where I looked, I could not find a replacement, or a center cut pattern of anywhere near similar plate thickness.
If I had, I would have had a machinist cut out centers of identical I.D. and O.D., and then had a welder attach the 2 good parts that I was interested in.
What I was forced to do instead was have the center of the bad sprocket's teeth welded in with new good metal, and then attempt the laborious and nerve racking task of trying to restore the teeth in the center of the sprocket.
First up was to drill, then final grind with a sand paper roll on a Dremel tool the exact I.D. of the center hole. No easy task for myself.
If you have a good machinist, they should at least be able to handle this part easily enough.
Next was the mission impossible task of filing the teeth without going too far and turning many hours of work into useless junk.
It started out with a traced pattern and very conservative hack sawing, and ended up with at least hundreds of trial fitments after learned intervals of filing, using machinist's blueing or magic marker applied between pattern displaying taps, which were hard to keep centered. This progressed to looking for the shiny spots on the newly filed proto- teeth that I initially filed with the slightest of taper.
Unaccountably, the clocking, or rotational alignment of the parts was seen to be important, and miraculously, perhaps a dozen hours later- I ended up with a better than new press fit.
A lot of work, and a little luck too likely at play here. So try to find a piece that you can have centers interchanged and then welded, and as a last resort, perhaps a watch maker would be more comfortable with filing new splines on a sprocket with a smaller center, as they are at least experienced at this sort of thing on a far smaller scale.