Here's the structure: There's about 2-300 individual branches spread out across the country. I'm following the Washington, DC branch, which is structured as follows: the leader, his younger sister, the big guy, their hacker, and the hero all know each other, mostly because the big guy is a very good tactician and the hero showed up half dead on their doorstep. The leader and his sister are the only ones who have ever even spoken to the actual head of the resistance or members of another branch. There's another 10 or so people under them who get called out for combat duty. As for getting in contact during emergencies: currently serving members are issued hacked and encrypted prepaid phones. When they're needed, a call comes out from the hacker, who randomizes the number every time. As for how they actually get these phones: new recruits have to go through existing members, each with their own ID number and unique verification phrase (which is usually along the lines of "you government bastards wouldn't know a code phrase if it kicked you in the balls" in order to throw off interrogators). The existing member vets the prospect before deciding whether to send him onto the head of of the branch with a letter of introduction containing just the member's phrase. The leaders then perform a second background check on the recruit, connect the phrase to its owner, call him to make sure that he's alive and did in fact recommend that particular prospect. If all of those conditions are satisfied, then the prospect is accepted into the branch. If any of the checks fail, the prospect will be shot.
My problem is getting prospects in contact with existing members in the first place.