Do you ever approach a stranger and tell them you think you could make some quality photos with them? If they agree would you ask for them to sign a release in exchange send them some of the best pictures?
I don't, but often think about it!
Problem is these days, people don't do much for free, and most will want to know the ins ad outs of what you plan to do with the image and what they can get out of it.
Just last weeeknd I saw a guy photograph a Street Performer who asked for $ and became very angry when the photographer walked away.