I'm not sure if this will help but I received a post several months
ago that the DuBois Center at Harvard was sponsoring a computer data
base on the slave trade - that is the ships, etc. This would include
info on the origins of "cargo". I believe David Eltis is involved.
There is also another one - a 10 year project sponsored by UNESCO
I'm not sure how far either has gotten but you might want to track
them down.
If you cannot find the info contact me privately. I think I
still have the old post about both projects. Or you might contact
Eltis directly. I don't know his email but he may be on "NuAFrica"