Metal manufacture suggestions?  

Pretty much all metal bases similiar to the above style are made by either die or sand casting aluminum.
In sand casting, a pattern (a slightly larger copy of the finished part, to account for shrinkage) is used to create two halves of a sand mold. Molten metal is then poured into the hollow cavity making a copy of the part. The part is then removed from the sand. There will be a distinct line/ ridge around where the two halves of the mold came together. This is referred to as the parting line. The surface finish will also be quite rough.
In die casting, two pieces of steel are machined into a "core" and "cavity". The core and cavity are a negative of the part to be produced. Molten metal is then injected into the mold and held under pressure until the metal cools enough. It is then ejected from the tool. The surface finish is better than sand casting.
Both processes do not produced finished the parts. After casting, the parting line and flash (molten metal the squirted out of the mold) must be ground off. The parts are then ground and polished to produced a smooth, mirror reflection.
Knowledge of the exact requirements of these manufacturing processes as well as skill with a CAD (computer aided design) package will be required. I happen to do this for a living, and happen to contract on the side.

Hi Lowe9,
Thank you!
That's been a great help.