I entered Vault 3 dressed as a Kahn to deliver some chems from Jack and Diane. (Great Mellencamp reference BTW)
and did a little exploring after dropping off the suspicious package. It turns out there are at least 5 or 6 skill magazines in the dorm section and a mini jailbreak quest. Worth the side trip for sure.

Also check all the mailboxes you come across in Novac and Goodsprings. Many of the have mags.

as you come off the mono rail and into vegas, thers 1 of every mag in the brown mag vending machines too

They are truly all over, you just have to be dilligent and be sure to search every room, everywhere you go. I've got more than I'll ever use.

Actually, lol, any faction or location that I have the highest status with, I visit their merchant often. They will usually have 2 or 3 magazines selling to me at value (20 caps I think). Buy em!