Caboose Hobbies in Denver has a lot of these in stock. I don't know how detailed their web site is to see, but it's
www.caboosehobbies.com
I agree not enough interest has been directed toward the possibilities these castings offer over the years. With all the talk about bad brass here a couple of months ago tis was apparent. I have two Sunset K-28'd that each carry a bunch of fine Backshop castings and look fine, particularly the one with the new PSC cab!
Mike