What are some good ways to find potential girlfriends for a poly relationship?

Keeping in mind that I don't know much at all about this subject...I would think that online would be best. You could at least get to know the person first before ever meeting them in person and you could develop a friendship with them. I'm sure that there are dating sites that are suited for your need, just google polyamorous dating, you should get some hits.

Also, you could bring your spirituality into this and request assistance in your search, calling on a Goddess such as Venus or Aphrodite.

You might also want to make sure that both you and your husband are in the same place emotionally. He might want to eventually find a third partner but I feel that there is a transition period where you know you will miss having that person all to yourself and then finally being ready to share.

If this is happening energetically with one of you or both of you, then it might effect you finding the one until that transition is complete.

Lastly, in this crazy world, it's hard enough finding one person to have a quality relationship with! ;) Be patient, it might not come to you in the direction you are looking, it could just fall in your lap at some social setting or something.

you might try some swingers clubs. its mostly about sex but they certainly seem open to sharing.