Far as I can tell, the intelligence community is a fork in the road on the career path to diplomat. You study languages, public policy, international relations, etc. You get State Department / vague US gov (National Security Language Institute - Youth) scholarships to fly to the middle east and learn languages over your summers. You do internships in college with State and think tanks. It goes from there. (This is probably more for analysts than field agents).

Of course, actual physical badassery is carried out by special operations divisions of the armed forces - you get there by being a really good soldier, sailor, marine, or airman.

The intelligence services do just have regular job boards, college recruiting, etc. too. And then there's private intelligence firms, which have some overlap with journalism (i.e. Stratfor and Reuters both sell intelligence services in addition to their publications).