Burger Bun Shangri-La?
I had read on Chowhound in a 2003 post that Puritan Bakery in Carson, CA supplies most notable SoCal burger chains (including InNOut, Fatburger, and Tommy's, among others) with their buns.
Interesting article in last week's Orange County Register about Puritan & their process:
From "The secret behind SoCal's best burgers" by Nancy Luna