Gears for wheel and axle assembly for Spectrum 1:20.3 Two-Truck Shay

[NormaJean]

I need to replace 3 of the 4 black plastic gears that are located in the middle of the wheel and axle assemblies of my two-truck Shay.  Does anyone know the SKU for the gears or, if I need to replace the whole axle assembly, the SKU for that?  Thank you!