These adjustable handles allow one to put a lot of clamping pressure and they adjust out of the way without loosening the pressure.

http://www.monroeengineering.com/adjustable_handles

Making the rest of the gauge should be pretty simple, one could even use a stable hardwood for the body and metal for the blade.
Big Timberworks did make some that are all aluminum and around 18-20". Not sure if they have any to sell though?