In Brazil you can get chromium oxide very easyly in any arts and crafts store that has suplies for porcelain painting. Chromiun oxide (in powder) is used to "paint" porcelain. You should get a bottle of copaíba oil also, as it is what people use around here to "dissolve" or "dilute" the chromoum oxide.
Oh, and the chromium oxide is called "Verde do óxido de Cromo" in those stores. Other thing: the copaíba oil will leave a really nice "woody" smell on your strop. I use Chromium oxide on a old leather belt to keep my kitchen knifes scary sharp.