Stuff on Aztlan and Amazonia can be found in Ghost Cartels, War!, and the Sixth World Almanac. All are SR4 books, but all the fluff is still valid and you may still find these books on game store shelves (perhaps even on discount racks) or in PDF form on DriveThruRPG.
Not a lot has been published for SR5 yet, but there's some stuff on trafficking along with the border crossings in the Coyotes e-book, and there's some fluff on what it means to be a hitman in The Assassin's Primer.