The armor is fitted with a back-mounted TX-28 MicroFusion Pack which generates an output power of 60,000 Watts to power the HiFlo hydraulic systems built into the frame of the suit. Made of a poly-laminate composite, the outer shell of the T-51b is lightweight and capable of absorbing over 2500 Joules of kinetic impact. The 10-micron-thick silver ablative coating can reflect laser and other radiation emissions without damage to the composite subsurface and the eyeslit for the helmet is made of bullet proof glass to protect the wearer from any projectiles. The armor usually carries enough fuel to last for one hundred years.
Black Mountain - two can be found in a radioactive crater southwest, on paladins Hughes and Fairbanks. If having only found Fairbanks (paladin with the logs), Hughes' body probably glitched into the side of the crater. About 5 centaurs, and Moe are holed up in and around the crater.
Nellis Air Force Base - two can be found just outside the base. They can be found while avoiding the artillery shells flying in one's direction; or gain entrance to Nellis then come back and search in relative safety.
Can be obtained from Hidden Valley if the Courier has the Mister Sandman perk and kills sleeping paladins. (Doesn't turn any BoS characters hostile), however, in a "Hidden" position, with a silenced weapon, the Brotherhood will turn hostile unlike any other faction even if members are stealthily killed.
Can also be pickpocketed from sleeping Paladins as they will remove it while sleeping. The Paladin at the shooting range, however, will not remove his to go to sleep. Also, the Paladins who sleep in the beds near the range are the only ones who remove their armor for sleeping. Note: It's almost impossible to pickpocket it, even with a Sneak skill of 100 or a Stealth Boy.
xbox360ps3pc Brotherhood T-51b power armor is much more common than intended, due to the armor occupying a list meant to hold Brotherhood T-45d power armor. Among other issues, this results in the dead paladins found in the quest Still in the Dark being attired in T-51b armor, rather than the intended T-45d armor. [verified]
ps3pcxbox360 If you give the armor to a companion to wear, and the response is "This follower will not wear this faction's armor," the armor might disappear. The only way to resolve this is reload a save. [verified]