After Market Rims

Ok, I am having a really hard time finding any rims with more than a 20 offset. Most are 0, 18, and 20. Not sure about the hub centric part but this is what I'm looking at. It has an 18 offset and indicates a 3600 lb rating.
http://www.wheelpros.com/wheels/MO975/MO9759?brand=Moto%20Metal&year=2013&make=Ram&model=2500%20Standard