The 2023 GTA 5 source code leak reveals a log of all the files found in the RPF archive (the file with all the sounds, etc.) of an early build of the Contract update, with a list of songs that were not included in the final version. Only the file names are known; it is unknown which artists performed these songs or what radio stations these songs were supposed to be on, but some approximation is possible based on the song titles alone:
Chief Keef feat. A Boogie Wit Da Hoodie - Glory Bridge (2017)
Chief Keef - It Ain't My Fault (2012)
Fenix Flexin feat. D-Block Europe - From the Block (2021)
Flipp Denero — Leave Me Alone (2018)
Freddie Gibbs feat. Big Sean & Hit-Boy - 4 Thangs (2020)
Pacman Da Gunman feat. Richard Fisher - Spin Again (2021) (Not entirely confirmed, it may actually have been a song from another artist)