Probably best bet would be Calsak Plastics in Duluth/L'Ville, but last I checked with them I think they only had white and metallic.
It's just polystyrene, so worst case scenario, you could always spray them with black Rustoleum. It's reef safe once cured, and a lot more scratch resistant than it used to be on plastics.
Source: I may have built one or two costumes.