Where can I find non copyrighted dubstep?

I think what you’re looking for is material with a creative commons license.
Try here

Specifically

Make sure the piece you’re using is licensed for derivative work for commercial use, and that you credit the artist.

I wouldn’t be surprised that you’re having a hard time finding free music that the artist is happy to allow you to make money off of. The musician didn’t pick their tracks of the cherry tree.

Make airplane noises into a cheap microphone?

Sorry, I’m a bad person.