Hi.
Seeing as you are experimenting. I assume will fit, is good enough rather than Tamiya branded
Carisma M14 R380 Pinion Gear for 2.3mm motor shaft 12t STANDARD CA14037 | eBay maybe this will do?
shows These are the Pinion Gears to fit the M14 range of Carisma Cars or any R380 motors. They will fit 2.3mm Motor shaft and has 48dp / 0.5 module
10t - 11mm long x 6mm dia
12t - 11mm long x 7mm dia
14t - 11mm long x 8mm dia