If anyone wants to find this song in-game, check the "3 Red Light keys" part of Allen's tape. When looking for 8-Bit tracks, look near the end of everyone's story, or in your case, backtrack to where it began near the end of the game. If you want one more hint, let me tell you that nothing gets locked off with progression, you just need to re-unlock it, even if the quest isn't marked.