i found the BoS bunker in hidden valley (which is east of Goodsprings). You need a 100 lockpick skill in order to get in. when you get in you are taken to Elder McNamara and you have to do a short quest for him. then you can trade with Knight Torres (she's next to the shooting range). you can choose to help her find the missing laser pistol. after that find Initiate Stanton ( he's usually in the classroom) and ask him about the Laser Pistol. He will tell you that he and Apprentice Watkins went exploring outside in a scorpian area when they got surrounded and had to run, dropping the pistol as they ran away. You can then go outside of the bunker to a place nearby called Scorpian Gulch, the laser pistol will be sitting on top of a rock next to a dead wastelander (watch out for the radscorpians). Go back to Knight Torres and give her the missing pistol. She will reward you with a tri-beam laser rifle. Job done, but there is on problem. When I turned off the game and then played it the next day, I went to her for weapons and she asked me for the missing laser pistol again. So I went to Initiate stanton and he thanked me for returning the laser pistol. I went to scorpian gulch again, but the pistol wasn't there. Knight Torres keeps asking me for the laser pistol even though I already gave it to her. Is there a way to stop this glitch? Please help me.
I sloved the problem. you have to do quests or other things for a while, then come back and ask Elder McNamara if you can join the brotherhood. you will do a queste for him, then come back and you will get power armor training and Knight Torres will stop asking you for the mssing pistol. also you will be able to buy anythng from her, not just the small things.