I believe the nitro revo cd tooth count is 28T while the erevo/3905 emaxx is 33T.
Check this site Linc. They sell composite gears.
https://sdp-si.com/eStore/
Go under "Gears" and then click on the "Composite Material, "Spur Gear".
Do I get a discount if you find what you need from this site



?