Lavalife is a dating site with three profile sections, dating, relationships and intimate encounters. Intimate encounters has many profiles with couples searching for a third person or other couples. Post a profile, exchange email, arrange a meeting. If the vibe is good, procede from there.
However a word of warning, someone very close to me was in the swing scene with his wife. They had done this for a few years. Eventually they decided to go exclusive with another couple. He fell in love with the other woman. They were both going to leave their spouses. However she had second thoughts and went back to her husband. He not only lost his wife, but the woman he believed was his soul mate.
Play with caution.
www.lavalife.com