Welcome to our forum.
There's a section of the boards here for looking for and meeting people; go to the bottom of this page (right hand side) and look for the "Forum Jump" menu. You can use that to jump to the "Dating & Friendships" area. Perhaps that might help you in your search.
What you're looking for is fairly specific (I think), so have some patience, it may take awhile to locate your "dream couple." In the meantime, have a look around here as there are a lot of good threads about making polyamory work.
A few external links you could try:
Some of the above are just links to local poly groups in your area. If you have any nearby, you could join that group and get to know some people in person. Also the following is a thought:
"If by some chance you are interested in anything alternative like renaisance fairs, goth culture, sci-fi conventions, indie music, bdsm, or any small fringe group, you will be more likely to meet people who have at least heard of poly and are accepting of it."
-- SpaceHippieGeek, http://polyamoryonline.org/smf/index...57394#msg57394
Whatever your interests are, if there's a club or something nearby related to those interests, that might be a place to meet people, although if they're not polyamorous you might have to tell them what polyamory is and see what they think about it.
OKCupid isn't specifically poly, but as a dating site it's pretty good about being open to gay, poly, etc.
PolyMatchMaker has a considerably smaller membership count than OKC, but at least it's specifically poly.
Perhaps something in this post will be helpful to you in your search.
Regards and well-wishes,