Or do they HAVE to be purchased? Also can you change your hair/facial hair like in FO3 at some point in the game?

i'm fairly sure i read in the manual deal that came with the game that you can find weapon mods in containers

Confirmed. I've found one laying about in my travels.

I'm pretty positive you can not, however, find haircuts in containers. There's almost certainly a barber somewhere, too, though I haven't run across him yet.

They seriously need a long hair style for men..........