Not much help, but I found two in really good shape at the local Pick n' Pull a couple of months back. $12 apiece. Don't want to sell them, just a possible tip.
I think you have to be lucky to find them. There's 3 outlets of that franchise in the Bay area and if you get lucky and get there when the rigs first get put out, you can score some chit. I wish I had a friend in one of those places who would call me when the models I'm looking for get put out. It'd be worth some beer money for the guy for sure.
I imagine you've already tried the specialty MB dismantlers. There a lot more spendy, but they have the stuff on the shelf, often as not.