The memory cards are located inside the "safe house" of each of the outposts listed below. Once you have liberated the outpost, search inside the building with the red door - the ones with the dispensing machines.
North Island
1. Orphan Point
2. Welshore Wrecker's House
3. Amanaki Outpost
4. Northview Gas
5. Rust Yard
6. Cliffside Overlook
7. Old Mines
8. AM 12
9. Hubert Shore Power
10. Broken Neck Home
11. Camp Murder
12. Kell's Boat Repairs
13. Nat's Repairs
South Island
14. Lazy Shore Marina
15. Bridge Control
16. Spine Ridge Site
17. Longshore View
18. North Kirge Crest
19. Maw Docks & Repairs
20. Satellite Communication Hub