I don't think you can ever get them that really shiny metallic color, but you can come pretty close. I did the topper for an anniversary cake in silver (sorry don't have a close up):
I colored my gum paste a light grey and then dusted with silver luster dust and lemon extract.
Try it on a few fondant balls and see how it works. I do have a silver glaze too, but I still don't think it's as shiny.
One thing you might do too is after brushing on the luster dust and extract, get some silver disco dust and coat them with that and see how that works.