I took a Cessna 404 from Libreville to Nairobi way back in 1985, when I had to go to Bangui to refuel for my next stop in Kigali. There was no Avgas in Zaire and that was before the place fell apart.
How about carrying along drums of fuel and a pump to land and refuel from drums?
About the only other option would be to pre-position drums of fuel but that's expensive, of course.