Well, as near as I can tell you have a few choices.
Learn to play an instrument (I'd suggest piano lessons because you can do a lot with a keyboard).
Find someone locally who is a musician and pay them to write the music for you or ask nicely as they may just want the exposure.
Search the internet for something called "creative commons" and music licensed under the Creative Commons license structure is free for use, editing, and in most cases only requires that you attribute them as a source if you intend to distribute the resulting changes you made to their work.