I hear ya, I am in the same boat. Best advice is patience, they do pop up from time to time. Set the money aside and be ready to pounce when you see them. Negotiate as best you can but expect to pay what they ask unless they do not know what they have or care.
Yes we do share rims with most 6 lug trucks, but, only the older versions have rims that will fit as most of these behemoths have gone to 20"+. I am currently running 17" Escalade rims and will going to billet wheels as soon as I find a set as well ...
Good luck and welcome to the hunt.