They run operations like Cicda3301 to recruit to ones that make it to the end.

https://www.cicada3301.org/

/s

Ok but seriously they fund things like USAMTS which I assume gives them access to a list of promising young Americans.

That's boring maths though. Great, they found some people that can do hard maths. Cicada3301 winners prove they have a wide range of abilities. You're "tests" would be fine for the NSA types that just sit in a gov't cubicle going blind on cyphers. CIA wants people that can figure things out without getting caught.

The parent comment asked about the NSA, and, well, they happen to do a lot of math.

I found Lex Friedman's interview with Nicole Perlroth discussion of hacker culture and the mechanics of creating and selling 0-days to nation-state actors interesting.

https://youtu.be/hy2G3PhGm-g

Aren't they famous for going to hacker conventions and looking like another fellow hacker instead of a suit? the NSA even has given talks at DEFCON.

You really think there aren't computer security experts from government organisations on 4chan? I thought half of its schtick was it was a wide range of humans from all walks of life, pretending to be (or actually being) whatever-it-is that humans become without any form of supervision.

I'd imagine direct and indirect infiltration. Hackers charged with crimes, who are part of a larger group, sometimes get plea deals. As part of their deals, they might give up accounts, keys, data, or evidence from the group, and/or work as confidential informants for the government.