Spooky is correct, its at the Pentagon AKA The Citadel, further on in the Progression of the main quest, where you are taught to wear Power Armor. The people at GNR as well confused me at first, but I found out that the dialog that they state was put there by accident as you cannot wear power armor til you are much further into the main story-line, sadly you have quite aways to go... If you want a good alternative to Power Armor at the moment tho, get to the Underworld near the Washington Monument and go into the "Chop Shop" which is the basic hospital there, wake up Reilly who is lying on the bed in a Coma. Do the Reillys Rangers quest, you will get Reilly Ranger Armor when completed, it is the best armor next to the Power armors and can be repaired with any kind of combat armor, it has 39 Damage resistance and adds +10 to Small Guns skill. Hope that helped !
