What you wanna do is get an African nation become modernised, and obviously avoid colonisation. They should at least be modernised to Thai standards or failing that, survive. I'd prefer for them not to be protectorates but if it's needed to survive, then DO IT.
Some possible countries:
Sokoto Caliphate
Madagascar
Kongo
Ethiopia
Morocco
Possibly the Barbary States
Bornu
Lunda
Some sort of Madhist state
Darfur
Zanzibar
Egypt
If you have any more suggestions for countries I'll edit in.
POD of 1700 or after
I know they might not all be plausible but they just suggestions (bad ones)
If you can have them be able to beat at least a second rate European power (like Portugal, I reckon) so a bit like Madagascar waring with Portugal and taking Mozambique. Also if you can have two or more not colonised and make some sort of anti colonial alliance with each over and maybe the Ottomans and Persia maybe they could help independence movements across Africa. Sorry for making this so long. Anyway if you can have win a war or have 2 or more survive and I'll post a pancake through your letter box.