There are 8 total across 3 missions. 7 are found around different locations and to get the 8th you have to solve the multiple choice on the computer after you FINISH the DLC
Multiple choice answers:
1st-3,2,3,1
2nd-1,2,2,1
3rd-3,2,2,3
4th-1,1,3,3
5th-3,3,3,3
6th-1,1,2,1
7th-2,1,3,3
8th-3,3,2,3,2