Quoted from mg81:

I would be stunned to hear that Bally/Williams had a custom made gear for this application. They likely used an off the shelf gear that was already available. Gears are so common for so many industries. Look at a supply company like Grainger (https://www.grainger.com) and see the available gears. Also, I would assume that Bally/Williams used the cheapest gear they could find, a few pennies in price actually mattered to them. But for one of us in the hobby paying an extra dollar or two for a high quality steel (or brass) gear would be no big deal, you could probably get a much better than original gear for a relatively low cost.
Even if you can't find a perfect replacement for the stripped gear you can probably find two new gears to put onto both shafts that are the correct matching diameter/tooth configuration so they will mesh with each other and replace the stripped gear and the gear that stripped it. Just make sure the two radiuses (sp?) of the gears add up to the right amount relative to the distance between the two gear shafts. So what if they are a slightly different ratio, the planet might end up spinning at 4.1 or 3.9 RPM instead of 4 RPM (or whatever it happens to spin at).
All of that said, for a single installation it might not be worth the time and effort to figure that out. Though for someone like Firebaall it might be worth while if you have a few you can repair.