Well, some people use chalks. Ordinary colored craft or artist chalks. The better quality art chalks are more intensely colored, while kids toy chalk tends to be pale and "chalky" :)
Chalk isn't metallic, but it will add color; I like to use it for flower petals and on tiny food to add "baked color" to bread or pastry, and such.
Any intensely colored dyed powder should work.
Otherwise, if you can get eyeshadow, it is about 80% mica powder. Or some art stores sell mica flakes, which you could probably crush and grind in a mortar and pestle or spice grinder. I'm not sure you could color it yourself, though.
I've been able to buy mica powders (for making your own make-up, in theory) from online sources. You might check to see if there is a beauty-supply shop anywhere; they might also carry some or something similar. Or be willing to order it for you.