I would post in the Help Wanted section a request. There could be a few composers who have tracks that can be used for free or for a fair price.

Royalty free music can be bought at a lot of places. If you google "royalty free music" you will find almost a big amount of options. Not being lazy to not post them here, but the choise is so big that it is better to look on google and see what would fit your needs.

Also some of the composers here sell royalty free music.

You can find my royalty free music here:

My royalty free music

Good luck!