Why not, you could add BoS Patrols walking around the center/sewers/exploring dungeons with around 700 hps and heavy guards, there could be like 15% chances to find one on the body of a soldier wearing one.
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For making it more rare and unique, there could be like 1/2 groups only that appears just in the weekends, that's your choice now if you want to make it display like a server message event, or not
EDIT : Now with the new changelogs, in my opinion, what about only by having got a training coming from a NPC from the BoS (Looks like BoS isn't present in AoP) so than, a NPC could be present for each factions, some ideas :
V-Tech : Ex-Scribe, An girl coming from the East that don't support the BoS anymore since the war with the robots and the mutants there, joined the V-tech because she is for the idea that the womens win the fight against the others faction. She can give the training for wearing PA for caps and High Rep (reference Fallout : Tactics.)
Brahmin Boys : Ex-Veteran Trainer, this old trainer was giving lessons before to the new initiates, in a Bunker located in the hills near the NCR, He's at the research of the Chosen One *personal reasons*, now need caps for keep travelling for his objective. He gives the training for caps and High Rep (reference to Fallout : 1)
Family : Ex-Initiate, back from the ruins of Washington, DC. Apparently this initiate was suppose to be promoted Paladin, but he gots captured by some slavers and after selled to the Family, He/she gives the training for wearing PA for caps and High Rep (or by making him free *suggest hard quest*) (reference Fallout : 3)
Lawyers : Paladin, coming from the Nevada, this paladin is one of the son of a grand-Paladin who a long time ago, made a town with a mutant in his young ages. Now he's giving the training for wearong PA for caps and High Rep. (Not much creativity on this last one haha, sorry).
