A number of people have suggested and/or modded various things in this area; one that can be modded without too much trouble is to give the East Africans their own tech group with access to cavalry. The problem with the rest of Africa is that the lack of cav had little to do with tech and more with the environment. i.e. it shouldn't really be possible to recruit cavalry there regardless of your tech group and cav should have an extra high attrition rate. You could create a decision to buy a cavalry regiment at high cost (imported horses). OTOH if a sub-saharan tech group country expands outside of Africa and has contact with cavalry-using neighbors they should probably be able to recruit cavalry there.
Some previous (old) discussion:
http://forum.paradoxplaza.com/forum/showthread.php?288152-Why-Africans-can-t-have-boats
http://forum.paradoxplaza.com/forum...-should-they-have-or-get-cavalry-Input-sought
http://forum.paradoxplaza.com/forum...9-Questions-about-East-Africa-and-Tech-Groups
The second thread will only be visible if you have registered your game. The first bug mentioned was fixed in Divine Wind.
