As already rightly said, carriers don't operate in a vacuum and need escorts. When the Royal Navy commissions its new carriers, they will be stretched to provide a proper escort group for them whilst maintaining commitments elsewhere. I can't see African nations being able to support both a carrier and the escort group. Carriers without the right support are just large targets.
If we look at early post WWII, then yes, a few nations might have managed to acquire one of the surplus CVL/CVE types at a decent price, but those would soon wear out and replacing them wouldn't be cheap. operating them would bankrupt most nations and be done only at the expense of the rest of their armed forces/presidential guards etc. Even if they kept going, they lose the ability to operate effectively as the aircraft they can carry become increasingly obsolete. As we creep into the more modern era, operating a carrier in somewhere like the Mediterranean becomes harder and harder. Even in WWII carrier operations in the Med were risky, but with the speed and range of modern aircraft and their ordnance it becomes worse. Even a few high speed attack aircraft with quite simple missiles is going to cause major problems for a small ex WWII carrier with a limited air wing and few escorts. Yes, the Americans and French do operate there, but they have the full escort group around them, a mix of very modern aircraft on deck, modern defensive systems, SSN's below them and land based friendly assets within range. They virtually own a huge bubble all around the carrier. Could any smaller state operate a carrier in that environment? Few if any of the East or West coast African nations need a blue water navy, and apart from the ego boost of having a flat top, the only likely use for them will be against insurgents or other African nations. That puts them operating within a known area, in range of land based aircraft. Realistically only South Africa, as part of a Commonwealth or Pro-NATO effort, could come close to justifying a flat top.