Sadly, Wilhelmina, you are right. I don't know of any collectors in Africa except at opposite ends of the continent - I used to subscribe to a few collector mags a few years ago and there were one or two in Cape Town and the odd collector in Egypt and Morocco.
Other than the UK the main interest in 78s is (in Europe) Holland, Germany, Belgium and Scandinavia, and outside Europe in the USA and Canada. If you're staying put, those records might well have to be buried with you, since their weight means that shipping costs will not be economic. (Unless, of course, you find a kind collector who will buy the lot and pay shipping.)
Best advice is to use the internet to fullest advantage; research collectors and see if anyone is interested.