stocksy does not take editorial, and I dont know if they have plans to do in the future. As for "real" people signing model releases - it is like with all stock shootings - building a relationship of trust or maybe hiring paid models for a shoot. Models dont have to be young super good looking actors. Many normal people will be happy to take part in a paid shoot. Many artist actually live in these countries,so they obviously have their own connections. And small businesses everywhere need images for their own business.
It is just like any other model shoot. You need to explain what you do and find people who are ready to work with you. If you want to shoot in a restaurant in Berlin or New York it is the same process.