A few weeks ago, someone was looking for a container buddy to South Africa in the Bushtaxi Forum, which is well known among Land Cruiser drivers - but he has already found someone. There is also an English-speaking section in the Bushtaxi Forum, you could have a look there. Or do you already know which agent you would like to ship with? They often also offer to arrange container sharing. I can recommend one and put you in touch with a contact person if you like.
For information about overlanding in Southern Africa, our OB Africa Ambassador Christoff
@Get Out GO is a perfect contact. He can give you a lot of useful information.