A new page on the approximate cross-sections, called profiles, of custom-turned wood guitar knobs can be found here.
Example: 
More will be added as the images are processed. Since the profiles come from pictures taken with a digital camera at the same distance from each knob, mounted on a 1/4-20 screw, they are all relatively proportional to each other, but may be larger or smaller than real size due to your screen size and resolution.