Below are the locations of the music discs in Chapters 10 & 11.
Chapter 10
9. The Oppressed
Purchase disc for 50 gil from a vending machine in Aqueduct 1 of the Sector 6 Sewers.
Chapter 11
6. Let the Battles Begin!
Purchase disc for 50 gil from a vending machine in the Maintenance Facility of the Train Graveyard.