You might want to download Scot Reader's "inside T206" (link below) which covers which cards come with which backs. He updated it recently, and it's free
http://www.oldcardboard.com/t/t206/t...?cardsetID=699
The green Cobb is covered on page 62. It comes with an Old Mill back and a Brown Hindu among others.
edited to add: Oops, I just checked and that link no longer works. Does anyone have a fresh link?