The classics work well for folks that want a dual purpose backyard chicken/flock for eggs and meat. Mostly Barred Rocks, Sexlinks(if you don't care about pure breeds), Australorps(not the most meat, but fast maturer), and the always around Rhode Island Red.
I don't know about selling big but these are some birds that are very hard to find and sell immediatly it seems to me cause I have been looking:
These need to be exhibition quality, these are all standards as I don't track Bantams.
Dark Cornish, actually any standard Cornish, whites are impossible to find.
Light or Buff Brahma
Mohawk strain of New Hampshire
White Rock
Columbian Rock
Heritage Delawares
Aseel, Black breasted red, or Wheaton
we have a man here in Colorado named Al Prado Jr. that exhibits White Plymouth Rocks. I do not have any idea if he sells any or if he is willing to ship any. He raises mostly bantam breeds (Cochins) but he does keep large fowl, just in small quantities. He raises a few of Exhibition White Rocks and Barred Rocks. He usually only shows white and black birds.