Don't sweat over the definitions - sometimes I think it would be useful to have a special word to designate a single looking for a triad that would carry less 'baggage' than unicorn, but we make do.
So now, hit the poly groups in your area. Try on-line dating if that feels comfortable (OkCupid is nice, I don't have experience with other sites). You might want to check out if there are any bi organizations in your area, just in case. If you already belong to a 'subculture', like the kink community, Neo-Pagans, gaming/SF, what have you, keep your eyes open while socializing in those circles. For me, meeting people through other people works best. Even coming out to a select few trustees and telling them what you are interested in might reap unexpected benefits.
(Just for the sake of illustrative purposes, I've met one partner through gaming, two through the local poly scene, both off and on-line, and two others through existing partners. So pure luck plays a large role in finding compatible couples/individuals.)
Me: bi female in my twenties