The best way is to just work through the specification and get case studies from that. The main case studies I use for Africa are:
Kenya
Nigeria
South Africa
DRC
Botswana
Rwanda
It may not seem like a lot but you really have to know them in depth across the specification. I know this isn’t much help but my teacher just gives us lesson plans for those topics so I’m loaded with notes for it and have organised my revision accordingly. But I hope this gives you a start of some sort??? X