How do I find a girl for 3way/experimentation??

Hubby and I have discussed this a lot and want to try another woman joining us but how do we find her?! Very small group of close friends, a couple girls but wouldn't want it to be either of them....how do people do this? He's always loved the idea of me with another girl and I'm open to anything. Have to work out specifics but can't do it without her.... Just don't know where to find her lol