You could try Architectural Glass and Metal off of choctaw or B&C Metals in Denham. They might be a little pricey for what you are needing, but its who we use at work when we need metal work.
I basically need a piece that will go around the top of my AR with an ACOG on it covering the trigger on both sides and a cup to slide the butt into. I am going to use a tufloc unit to lock in the barrel. On the base it will need to have one step up of about 1/4. I am going to mark and measure it up as soon as the tuflocs get in.