I know where you are coming from. I am an atheist who was in a BDSM type relationship while living in Georgia. We talked about polyamory, but we never knew where to start. There are some polyamory groups that meet up. You can find some on social networking sites and hope one is in your area. There are some dating websites that may help. They are in some of the other threads on this board.
I recently talked to someone who went to my high school in Georgia. I found out that he and his wife are polyamory atheists, but they are deep in the closet. So I imagine that there may be many people around you that are hiding it as well. Sometimes, some leading conversations may show you who is in the closet.
Also, if you are into podcasts, you should check out Polyamory Weekly. The host is into polyamory and BDSM.