I have a new batch of camera mounts for sale. I made some with a slightly smaller bore to fit standard 28mm railgun barrels, and some with a larger bore to fit the Rob Allen, Mako Iconic barrels, and other barrels that are roughly 29.5mm outside diameter.
The clamp is made of black Delrin, with a plain aluminum arm. The knob which attaches the camera is 1/4"-20 thread, and is retained with a snap ring so it won't get lost. The black rubber pad has 3M VHB tape on the back, but is shipped loose. That way you can position the camera arm the way you prefer, either like it is shown or flipped to mount the camera higher. Then just stick on the pad.
Price is $55 each for either size, and includes Priority Mail shippng in the U.S.
My email is: jdd@eatel.net