Charcoals are a type of Ebony. Ebony refers to a phenotype - any chin with a solid, wrapped belly. There are many different mutations that produce this phenotype - some are dominant, some are recessive, at least one is accumulative. The Broucke charcoal is a recessive ebony mutation.
At some point in chinchilla history, breeders stopped keeping track of which ebony mutations they had and/or bred so many of them together that they could not determine the genotype of the offspring. Thus, the majority of the ebonies in the United States have an unspecified genotype - we just know they have grey/black bellies. The Broucke Charcoal mutation very well could be floating around in the US, disguised because it is a recessive, we may never know.
Claire D has charcoals that have not been bred with other ebonies, a few other breeders in the US claim to have them as well but are not forthcoming about them. Others may say they have charcoals in order to sell an ebony.