I got all of the raid ones. At least those drop sometimes, just need to win roll against 7 other people. The hardest ones in the game to get are The Ancient City (lost city hard) and Upon the Rocks (pharos sirius hard). These ones you can do 100 runs and never see drop once.

City was added in patch 4.3 and I tried for 4 months, sometimes running it several times per day with no luck. Ended up buying it for 4 million gil recently. I cannot buy the pharos one which was added in patch 4.4 because none are on my world marketboard.

Unless you are extraordinarily lucky you need extreme dedication to get these. The devs really don't want people listening to these songs for some reason. They started using massively worse drop rate for certain dungeon songs this year without warning compared to how easy it used to be to collect music. It's akin to drop rate of getting legendary weapons in other RPGs. I had friends helping me out too trying to get the lost city song. It was sitting at 7+ million gil on my world marketboard for months.