There are so many bisexual or unicorn dating site which tend to cater group sex, but many are don't have certain goal for what people would like, straight people, gay, lesbian have their own dating tendancy on gay bar or lesbian site, but for swinging people and who want to be unicorn with open-minded couples, I recommend unicorndating.org for your best choise, because their main goal are find someone with open relationship, try it and discover your interests on this site.