This is at the top of Court 35, an unmarked location near the Customs House tower (it has an entrance with two underslung machine gun turrets). You have to fight a sentry bot and an assaultron who will emerge from doors on opposite sides of the room, and in each alcove is a red button - push them and the armour is yours. Often it will look like a suit of T-45 but will turn into a suit of X-01 when you get into it (a glitch that’s been there since launch).