What cards are you missing?
All are in the game. You have three ways of getting the cards.
1. Hunt them down in open world play.
2. Kill them on missions or bounties.
3. "Cheat" and go to the spawn point south of the White House pond. Named elites spawn there every 30 minutes. Keep killing them until you get them all. - I call it a cheat because its such a lame way to do it. I did the last few that way and its just not fun.
They are MIA in the storyline currently. We only get their lore data once we kill them but with them missing we won't be able to obtain them yet.
We know Mayham was in the stronghold preparing defenses but we never encounter her which leads people to believe she escaped before the stronghold fell the the Division.
Zodiac fate is unknown as he is not seen in the Stronghold nor was mentioned to be there. He could be alive or dead since he has a strong drug addiction.