The casettes can be found on different missions. Collecting all 12 of them will unlock the "Information" trophy/ achievement. There are at least two tapes that require specific steps and conditions before you can get them.
Casette #1: Complete the "Intel Operative Rescue" side op.
Casette #2: Found on the table of the central watchtower in the Administration Building. This is available in the "Ground Zeroes" mission.
Casette #3: Given to you automatically after rescuing Chico during the mission "Ground Zeroes"
Casette #4: Rescue the unmarked prisoner in the Western Refugee Camp. He's located under a shed to the northwest of the camp during the mission "Ground Zeroes"
Casette #5: This requires a couple of important conditions before you can get it.
- You must do this before loading Chico to the chopper. You can free him from his cell and bring him to the RV but don't call in the chopper and load him.
- You have to reach the boiler room where Paz is held without triggering any alarm. Your objective is to have the three guards needed to be in front of Paz's cell. Alarms will prompt them to leave their posts. If this happens, reload the checkpoint.
Head to the boiler room where Paz is held and you should hear the three soldiers talking about a recording they threw away. As long as you don't alert any of them, they should have this conversation. Otherwise, you have to reload the checkpoint. Head to the northwest of the admin building and climb up to find Chico's Casette #5 in one of the dumpsters in the dead end alley beside the stairs.
Casette #6: During the mission "Eliminate the Renegade Threat", enter the armory in the south of the warehouse area. This is marked by a red door.
Casette #7: During the mission "Destroy the Anti-Air Emplacement", rescue the prisoner in the boiler room. He's located in the same cell where Paz is held.
During the "Classified Intel Aquisition" mission, wait until the truck stops right outside the Administration Building. Sneak to the central watchtower and pick up the intel there.
Classified Intel Data:
After picking up Agent's Recording from the Central tower during the mission "Classified Intel Aquisition", head to the boiler to find a bald guy walking around. You need to sneak behind him and restrain him. Upon restraining him, interrogate him to make him drop the tape. If you accidentally kill him, reload a checkpoint.
"Here's To You" song tape:
Found in the cell adjacent to Chico's cell.
"Resurgence" / "Theme of Tara" Song Tapes:
This is during the Deja Vu (PS3 only) or Jamais Vu (Xbox only) Extra Ops missions. After starting the mission, go to the northeast (the safe landing zone) and watch out for directional mines planted along the way. You'll find a casette tape on the rock right outside the cave. Backtrack to the starting point and head towards the prison camp. You can get a shotgun in the back of the truck. After that, make your way to the southwest first.
Zone of the Enders: The 2nd Runner - Beyond the Bounds
Complete every mission on Hard.