I was in your situation once. When I met someone, or a couple, I'd let them know, in words, I that was married. If they stayed, I'd express my interest in various other ways. :p It worked most of the time.
Good luck. :)
I know its not easy being single in this lifestyle. I was there. . . But it is not impossible to find someone/couple even if you are a single. To what other mono single does, except, you have to let them know you are poly. Sooner the better.
Wish you the best. :)