PCPRO
What I have typically done in the past is purchased hot rolled steel plates and just drilled holes or slots in them so a camera plate screw can pass through them. You can purchase plates in varying thicknesses, usually up to at least 1". Then you can either cut/drill them yourself or have someone that works with metal do it for you.
A 3"x6" plate that is 1/2" thick will be around 2.5 pounds.
