I just bought a set of these from yorktrains. Not cheap but not more than other listed 2012 cataloged items. Maybe they have another.

You got to get in the trenches. I have some engines with 5 different numbers.  I dont lash them all together but since i like the railroad, i have dual engines pulling a number of different consists.  I guess im lucky to have my local hobby shop that will contact me when they get in additional ones i need.  Or get out there and hunt them your self.

I was at yorktrains today and had a gear for williams $5
I dont know if they are all the same or that it was for a U33.
You could give them a call, if you want to repair it.