Here is what you do:
1. Max theft or whatever and small arms (whatever it's called)
2. Walk down to the trading post.
3. Attempt to steal the Bozar rifle. Reload until you succeed.
In San Francisco. It was (AFAIR) in the lower left corner of the map. Like I described, you could get there easily straight from starting location, if your "A" mashing skill was good enough.
Not sure how you could get power armor early.