Okay, here are all the ways that my girlfriend and I have found other girls to hook up with:
1) My girlfriend tried to meet platonic female friends online via craigslist. She met a girl for coffee and immediately liked her. My girlfriend told this girl about our relationship and seriously talked me up. Then, my girlfriend invited us both out for drinks and told me to flirt with her. Easy enough.
2) Went to a beach and befriended some college-aged kids who were by us. We ended up making plans to go drinking with them later that evening. They were really cool and we all got very drunk. At some point, details of our relationship spilled out and one of the girls got very interested. The girl pulled my girlfriend aside and asked her a lot of questions.. then they started making out. It was pretty much a done deal after that. All I had to do was not screw it up.
3) We had a threesome with another guy who was exceptionally good with women. He basically referred us to every girl in his social group and it has yielded us SEVERAL threesomes with cute girls (with more to come). We call this "referral game" (I wrote a post about it here:
open-relationships-amp-referral-game-an ... 40407.html). Building a poly-friendly social group is BY-FAR the easiest way to find consistent threesomes.
The common themes among all these is that we flaunt our open-style relationship. The people who are interested in getting in on the action will be intrigued and will ask a lot of questions. Add a little bit of alcohol to the mix, then, at the end of the night suggest an after-party at your place (or something like that).
It's important for your girlfriend to let the other girls know that it's very socially acceptable and that she's just as much into it as you are. Girls trust other girls; they don't trust guys.
Anyway, I hope some of that was helpful.
-Wolf