Get friendly with people. When I was into winemaking and needed to source fruit, I'd find a vendor in the market or even roadside and start a chat. If they had any fruit too ripe to sell, they'd offload it to me by the flat/crate in exchange for a few bottles of homemade wine later on down the road. They'd be even more receptive to me when I made good on my word and stopped by just to drop off some wine.
I'd assume the same would work with bartenders or owners if you chatted them up and asked them for bottles in return for some homebrew. Most bars I know don't get a dime for their glass - it ends up in the recycle bins and gets collected by the city once or twice a week. What could it hurt? Plus if you churn out some good beer they could give you regular access to the bins. It just depends on the people and how good you are chatting them up.
The only thing I would advise is to be careful and extremely selective when choosing bottles from a bar. Unlike with a residential unit, which shares its bins with other recyclables such as cardboard and plastic which can absorb impact, bars and pubs have bins exclusively for glass and often get chucked in - hard. If you learn the neighborhood's collection days from the bar personnel, you can then access the bins right before collection day when they are full and have the least chance of fracture. You don't have to pick and choose on site, bring dozens home and clean/delabel them. When they are spotless, examine them under a bright light and check for microfractures. Bigger beers often have thicker bottles, which means unless you are hurting for bottles or specifically want them, stay away from twist-offs.
The more you brew, the friendlier you become. Use this to your advantage!
