Drill a 1/8" hole down the riveted end. Squish the peened-out wings of the rivet together with vise grips. Punch it out. Take the gear to a small machine shop and ask for a flat disc of delrin bored and machined to the same OD. Trace the existing gear onto a piece of maskiing tape, slap that on your disc and bandsaw and file the profile.

It's a 9 tooth gear with what looks like a 14.5 degree pressure angle. A dividing head (and I'd guess module 3 cutter) will get you very close if you have a milling machine. You don't even need to have dividing plates because with 9 teeth your divisions are bang on 40 degrees apart- you could just paste on a printed sticker of a protarctor and work to its lines. http://www.banggood.com/8pcs-Module-3-PA14_5-Bore22mm-1-8-HSS-Involute-Gear-Milling-Cutter-p-1012467.html