I get mine from a couple places.
Sometimes I’ll find a song through YouTube with AMVs, MonsterCat, FunkyPanda, etc. I’ve found a lot this way.
Another good way (but not necessarily reliable) I’ve found is getting lucky with the music that’s playing in stores or in a public area and using the Shazam app to get the artist and song title. This has saved me many times lol
And sometimes I’ll get recommendations from friends, or even recently, I heard some good songs from the SZ Discord karaoke channel, so I’ve got a good few sources.