That's a hard question to answer- do you have a region within Africa that you're particularly interested in? Africa is truly massive with very diverse groups...
I've found the Opsrey 'Warrior Peoples of East Africa' book to be pretty useful although it has some overlap with the Foundry books. I presume by Chris Peers books you refer to the two Foundry hardbacks? They're essentials for the period. Digging into the primary sources is probably necessary for many tribes, and you won't always get more than what Peers gives. Researching 19th century African tribes is tantalizing.