I have added a camera bag to the list of items for sale in my online shop. http://www.camerabeanbag.com/Camera_Lens_Bag/p2203723_10890697.aspx
It is designed to carry a single large telephoto lens and I have keep the weight down to a minimum. I wanted it as light as possible so as not to add to the weight of those already heavy lenses.
It will take a 500mm f4, 600mm f4 or 800mm with a camera body attached. Please take a look at the link above.