The MondoClamp product line is a modular set of machined aluminum components that can be used to build super-strong, custom mounting solutions. It's like an Erector Set for making mic stand clamps. The set has been designed for maximum rigidity -- absolutely no wiggle, bounce, or droop -- even under heavy loads.
Before looking at the components individually, I suggest you start with the MondoClamp Assemblies page to see what kinds of things can be made from them. You might find something there that solves your problem without the need to build it yourself, and the assemblies are discounted relative to buying their components individually.