If you're already doing this, you probably have the skills and the tools to make your own molds (3D printed in plastic even), mold a rough version, then mill it

If you're already doing this, you probably have the skills and the tools to make your own molds (3D printed in plastic even), mold a rough version, then mill it down to proper tolerances. If your molds are good enough, and your pour goes correctly, and your tolerance needs aren't that high - the part that you get might only need a minimum of cleanup (sprue removal, some filing or sanding, sand/bead blasting).