Self-Addressed-Stamped-Envelope.
Come on, Steve; these youngsters don't know all of this snail mail stuff!
Instead of asking for submissions, and having to weed through all of them, do a search for what you want. When you find what you like communicate with the artist/band/whatever and ask if you can use it in your project; very, very few will say no. It's more work up front but a lot less on the back end, and you'll wind up with something very close to exactly what you want.
If you're looking for a composer there are plenty of composers forums where you can check out links to their music, and then ask the composers in which you have interest. Unless they're well established you'll get very few refusals, and if your project is exceptional you'll might even snag an accomplished composer.