Well polygamists are people who believe in one husband with more than one wife.The correct term for this is polygynist but polygamist is considered interchangeable. This is usually a religious practice and at this point in history is mostly associated with some Muslim and Mormon sects.

I think the term you are looking for is polyamorists. These are people who don't place much store in the gender of the players but focus on building meaningful relationships with others while in long term relationships.
Generally, depending on the climate of where you live, you can find poly grouping though the internet, in alternate news publications or through word of mouth. It's still possible to lose your children or your job simply because of your lovestyle choice so many of us are rather closed mouth about our relationships.
Some of the larger groups advocating for freedom of love style choice are the best places to meet people who are interested or active in the lovestyle.