I recommend finding someone you know who does music and gives you permission. Or someone you know's friend, or a local band or something. There are a surprising number of people out there who make really good music under the radar, and most would love to get it out there in something like this.
You need the creator of the musics permission to use it in your trick. "Royalty" is the money that is paid to the artist who wrote the music. If it is "royalty free" it means the music can be used for free. Does that make sense?