I very much doubt that any shanties were created in the slave trade. Britain outlawed it in 1807 and the United States in 1808, long before we have any evidence of shantying. If blockade runners sang shanties after that, they would presumably be the same shanties as others were singing.

The only shanty verse I can think of that appears to relate to slaving is the one about "black sheep that have run the embargo." But no complete shanty is devoted to the slave trade, and I don't know how widely sung even the "black sheep" verse was.

One could go "down the Congo River" for many things after 1808.