Its actually pretty easy to get this armor, I think, at least.
Get a Stealth Boy, go to a place where there are a Veteran Ranger(I guess thats what you want), make sure you have a silenced weapon like a Sniper, first of course buy the silencer for it, use the silencer on it, then you go behind a Veteran, use the Stealth Boy, and VATS the Rangers head, no karma loss or reputation loss if you get a sneak attack, once the Ranger is dead, you just loot his body

You can do this to get any armor you want, I guess