OK, Second Amendment Foundation. Try them.
As far as investment return from the NRA, I kinda like the idea of an 800 pound gorilla fighting against the idea of limiting the 2A. Besides they are the driving factor in the general "constitutional carry" idea that has started and passed the state legislature in 12 or 13 states.
But tell you what, join one of them for a year. Scan a copy of your membership card and I will reimburse you that membership fee. i think the info they share on what they do will convince you to keep your membership going.
NRA or 2A Foundation, your pick.
Nemo