Websites like filmmusic.io or soundimage.org have a decent selection of music you can choose from that are often used in jam games. It can look a little iffy if you're using the same music as someone else, but there's several hundred songs, so you can probably find something fairly unique and that fits your games.
Both websites run under Creative Commons Attribution, so you're free to use the music commercially or non-commercially, as long as you credit the creator how they request.