I use the free music from uppbeat.com. Here are the links.
Main Menu Background Music: https://www.fesliyanstudios.com/royalty-free-music/downloads-c/8-bit-music/6
Game Background Music: https://www.fesliyanstudios.com/royalty-free-music/download/retro-platforming/454
End Menu Background Music: https://uppbeat.io/track/kevin-macleod/bit-shift?_gl=1*9mj7g1*_up*MQ..*_ga*MTA4NjIyMTE2OS4xNzA5NDk1Mzk0*_ga_J12MEFBDB7*MTcwOTQ5NTM5Mi4xLjAuMTcwOTQ5NTM5Mi4wLjAuMA..
Game Over Background Music: https://uppbeat.io/track/danijel-zambo/game-over?_gl=1*8183l4*_up*MQ..*_ga*MTA4NjIyMTE2OS4xNzA5NDk1Mzk0*_ga_J12MEFBDB7*MTcwOTQ5NTM5Mi4xLjAuMTcwOTQ5NTM5Mi4wLjAuMA..