Furthermore, how do I receive Power Armor training? I've done the main quests for them, including finding the patrols, finding the scouts, and repairing their bunker. What can I do now? The only thing I can think of is finding that laser pistol. Can anyone help me?

I also had the same issue, and couldn't find the laser pistol...

I am going to be VERY angry if I have to start over simply because I didn't make the head Paladin elder...

You SHOULD be able to get PA training from that. Maybe try talking to Taggart in the VR Sim room? It'd make sense you'd have to go into a sim to learn it.

Worst comes to worst, you can always console command it. I thought there was another quest after repairing the bunker, though; did you talk to McNamara again?

Yup, I just got it myself. I went to the BoS safehouse, waited a day, and then came back to talk to McNamara and he gave me the last quest, which involves going to Black Mountain.

Once you complete that you get a suit of T-45d and Power Armor training. You can also then buy PA from the quartermaster.