They upvoted my answer and left a comment, and it almost made me wish I hadn't helped in the first place.
I was going to write something along the lines of: "You're looking for people that the market has, for some reason, undervalued. Primarily, this will be because they have some messy characteristic that companies systematically refuse to deal with. Historically, this would have been "not having a degree" but that is increasingly something that companies aren't undervaluing anymore.
The classic 2, that you might have more success with, are ex-cons and immigrants.
If you're looking for the 'diamond in the rough' then that's where I would recommend starting.