Hi. I see a problem with what you and your husband are looking for. You seek a "unicorn." Do a search here with that term to familiarise yourselves with the concept.
Dating is hard. Most poly couples date independently, and seek separate partners. Finding one person who will meet the needs and desires of both of you is extremely hard, if not impossible. Hence the unicorn term.
A hot bi babe (HBB) who will be into both of you equally? This can and will cause envy and jealousy issues. What if she likes one of you more? This almost always happens. What if she doesn't like 3way sex? What if she is envious of the sex, the dates, the other intimate times you two have when she isn't there? What if you two discuss her when you are alone together, but she doesn't get one on one time with either of you?
The problems are endless.
Please read this:
http://davidlnoble.livejournal.com/176039.html
After you have more fully informed yourselves about the problems with unicorn hunting, you may change your mind about finding a "girl" to be your "third" to "bring into the relationship" you already have.
Poly peoples' dating pool is small. Only seeking a woman who is willing and able to be your shared gf, and she isn't allowed to date anyone else either, even though you two can go on dates together... it decreases your dating pool, and it's just unfair to the women you seek. Many unicorns who try to get involved with a couple end up being used as unpaid housekeepers and babysitters. There are endless stories here from women who have been mistreated this way.
The only successful triads are those where one person of a couple meets and starts seeing one other. Then she may fall for the other person of the couple as well. It may become full on lovers/partners. It may become FWBs. It may be unsexual and just a good friend. But once in a while all the pieces fit and you get a successful balanced triad.
Much more common is a V. Say you meet a woman and you click. She isn't interested in your husband. You are then the hinge in V. Likewise your h might meet someone, and then he is the hinge of his own V.