I do a lot of threesomes in this lifestyle, and used to do many more on my own time (the scene of civie sex just isn't doing it for me lately).
Yes, a lot of us ladies know each other. Personally... and intimately

There are ladies in this lifestyle who I was friends with before we found out about each others secrets, and some that I've met here and hit it off with. I've dated more women than men in my personal life, and those girls that were in my life long enough to share this with have enjoyed it as well (I wouldn't consider them "one-offs" as two have stayed in this lifestyle since dissolving our relationship. Thankfully I've never been asked to do a double with an ex!).
It's not totally uncommon for a girl to see another girl's site, style and location, get talking over the course of time, and meet out at the bar for a drink if schedules match up. I hit happy hours at the bar with my more amenable coworkers at the civie job, so why not here? This lifestyle can be very isolating if you let it be - and there's no reason to let it be if you don't want to. the ladies here are for the most part accomplished, intelligent, and liberated, and therefore make great likeminded friends
Sexuality being what it is though, it's not just like I crawl into bed with every nice girl. Sometimes there's a spark, and sometimes just great company. When there's a man involved, his preferences obviously matter too! So, while I can tell him which women I mesh well with on the mattress (nothing tops good chemistry), the choice is ultimately his as to who we see. I've met great women that way as well - you men have wonderful taste! I love it, it's like a lesbian blind date, lol.
~Mme X~