I have never heard of these guys until I was talking to a lady on the phone the other night who had one. This is about the only site I could find them on, anyone know anything about them?
http://www.avianweb.com/bluebackedparrots.html

Hmm, no I haven't, how interesting, they look like a cousin of Ekkies in some ways to me!! Avianweb is great for finding out about all these gorgeous birds that I want and will probably never have... like the purple-bellied parrot, gosh those are my favorites!

The lady that had one said they were closely related to the Ekkies as well as the Great Billed parrot. Now I have to go look up the Purple Bellied parrot

I saw a breeder who had a pair (or two?) of Muellers. I mistook them for the Great Bills, although then again the pics weren't the best and I believe those were front shots?

Yes they do look a lot like the Great Bills. In my research for more info I found one for sale for $6000, I guess that is why you don't hear about many people having them.

I actually saw a great billed in person. A female. She was going to be shipped to another breeder to be paired up with a male. I didn't care to keep in touch with the breeder who had her (I wasn't their for myself but with a friend looking for a zon) so that's all I know about her.