Two things.
If you want to experiment with airsoft, you should head to
http://forums.airsoftmechanics.com/
If you want a cad file of a gearbox, good luck. The few people that succeeded in doing a *good* gearbox, are holding preciously on the file. "MtHaynes" is an example of this. He was producing true CNC gearboxes, and won't disclose the file, unless you have a rather large bank account.