It is not easy meeting other poly folk or people who may be interested in polyamory. Sometimes you can take a chance on meeting someone out of a polyamory context and see if they are open to the idea. I heard that sci-fi and comic book conventions are very poly friendly as well as pagan festivals or any sex positive group.
You could also try some kind of dating site like okcupid.com. But I think the best thing to do is just put yourself out there and make yourself available. Relationships will open up if you allow youself to be drawn into them. You just have to meet people and see where it leads.