Music hacks for Super Mario Bros I found on a Japanese site. Since nothing else is modified, they appear to be open-source and free to use.
Super Mario Bros. (JU) (PRG0) [!].nes
CRC32: 3337EC46
MD5: 811B027EAF99C2DEF7B933C5208636DE
SHA-1: EA343F4E445A9050D4B4FBAC2C77D0693B1D0922