Yeah I don't think bumping into random people in public places is a great strategy. It's not a social situation, and it's a complete crapshoot.

I think the best thing is to have a hobby or interest that has a local place where you can find other people that like it. Music is a good one, go to some shows by yourself and talk to people. Or tennis courts, a makerspace, some kind of special event, etc. You will already have something in common and something to talk about with the people there.