Every time you go to a bar or a club, remember to ask girls a question when you are having a conversation, "have you ever kissed a girl before?" If she says yes, that might mean she is your swinger girl. If she says no, maybe you should try this question with another girl.
As a matter of fact, there are more bisexual girls than you can ever imagine. All you need to do is keep looking. No matter what kind of girl you ask, you can find that they will be more or less interested in having a FFM threesomes with you if they have experience in kissing girls before in their life, or at least they are serious about it.
Nowadays, more and more women are becoming adventurous. Many of them may even do not realize the fact that they are bisexual until they try it. There are many examples like this if you take a notice of the girls around you. Once they ever kissed a girl and open the window of bisexuality, there is huge chance that they might like it. Therefore, even if they never kissed a girl before, you can even change the fact. Get them exposed in the right atmosphere with the right chemical, they will be surprised by themselves.
I take myself as am example. Three years ago, I had never kissed a girl, nor did I think of it. I had a friend who was a lesbian. She showed great interest in me, but I never thought about it. I reckoned myself as a super straight female until one day. She took me to a gay bar and we had a lot of drinks. It was the new year eve. When the clock rang, everybody was kissing someone and most of them were kissing people of their same gender. My friend looked at me and used her eyes to ask my permission. I felt a strong chemistry, but yet I did not answer her. She moved close to me and looked in my eyes and then kissed me. It was amazing. I guess it was caused by the atmosphere. I was in love right away. I could never imagine a girl's eyes can be so attractive. I liked her a lot. After that night, we were in a romantic relationship, but still, I was interested in men too. That was when I realize that I can be bisexual.
I am not saying that every woman can be bisexual. My point is never be so definite about yourself and other people. Therefore, if you find a girl who kissed another girl before, you can take her to get another girl. Then you can have a threesome dating together. But be careful, having threesome tinder hookup with strangers can be dangerous. Wear condom unless you want to catch STDs. Good luck to you.