Search the indicated location to find the corresponding magazine:

Bargaining 2 (lowers pawn shop items cost by 10%): In security box #145.
Gambling 1 (significantly increase your chances of winning money): In Palisades Mall, on a table above a pool bar, where you go down the slide.
Gambling 2 (significantly increase your chances of winning money): On a ledge on the left side of the top floor of Bennie Jack's BBQ Shack in the Americana Casino.
Gambling 2 (significantly increase your chances of winning money): In security box #304.