There's probably no official way to request a tour, no. So it's not "legit".

It's more about taking initiative and trying to connect with someone who works in that space, has some available time (this is the biggest obstacle but plenty of folks have some time), and appreciates it when other people express a passion or appreciation for their work or craft (which applies to most folks).

An easy example is that fire departments will often let kids come and check out the ladder trucks. They'll even bring them out to public places like a grocery store and let the kids get super close.

I doubt it, honestly. All of those places are have walls. They are critical infrastructure and "just looking around" sounds like a reconnaissance trip for a domestic terrorist in the making.