Nope, but Return to the Road of Kings holds a lot of information on the Black Kingdoms that weren't present in the original Road of Kings book. There are some 80 pages of new material, mostly on the Black Kingdoms. In the somewhat underrated Conan Compendium (a collection of early S&P articles and adventures), you'll find an article on the Spirit Eaters of Darfar, along with a Black Kingdoms adventure.