How/where can I make or get a professional "metallic" CD label?

We've been able to achieve that look I think you mean by reducing the percentage of the color in question - it had to do with dot density - how many dots within say a square inch. For a pantone color - say a dark red - but instead of having it set up as 100% we reduced the coverage to 40% and it allowed the silver of the nature disc to come through. Other ways are to set it up in CMYK or full color and then NOT have white underneath it - then the metal or silver again comes through. We also tweaked the contrast to reduce the vividness of the color so the silver would show through. Your options increase if you're professionally pressing them. If you're having them duplicated your option is to use the CMYK and have it printed on a silver disc.