True...but I still think comexxx.com can be your first step in finding other couples who swing. Just tell your gf that you have to take a sacrifice for the relationship and participate in one of the comexxx events to find willing couples to meet your gf and you at a private arrangement or take her along. Comexxx has a particular event called "Couples Meeting" (check
link) which may be suitable for you.
Reply to Klueze:
According to the comexxx website, single members can join. Please refer to this
link. I personally never joined as I have a SO and I don't think she wants to share me with anyone else.