where to find/buy/thrift old magazines

Kind of a random question but I like to make collages and use magazines for them. I would prefer to get them for cheap because I'm just going to cut them up, so it seems like a waste of money to buy new magazines off the shelves. Where in Houston (preferably in the loop – I live in Montrose) can I thrift or find magazines without having to spend money on new ones? I don't recall seeing magazines at Goodwill but maybe I wasn't looking in the right place.