I tend not to approach mono people for poly relationships. In fact I tend to avoid them like the plague. The drama.. the feeling of being the teacher, the parental responsibility over their mono feelings.. too much work for me.
When I was just in it for the sex.. I approached mono people all the time. The boundary of non-monogamy is a lot lighter when its just fucking.
I realize I have created a potential boundary to a set of people that may be able to work within the constraints (or freedoms) or a non-monogamous relationship. I just don't want to put in that kind of work at the very early stages of a relationship.