Okay So I read "The threesome Handbook" Which is not necessarily on just polyamory but a fantastic book in my opinion for beginners who are interested and would like to know what else is out there. The author put a lot of self research in and has a down-to-earth tone in the book. In other words, she doesn't use big words and even gives a few sex positions! Where to pick up thirds and etc.
Bought it at Annabelle's in Sioux Falls, SD. You can also get it on Amazon!