With regards to the original post,

375 H&H will work for all plains game here, otherwise for most 3006 is always a good option with 180 to 220gr bullets.

with regards to ammo, if you are coming to South africa, bring your own, as you cannot buy ammunition in South Africa without a valid firearms licence for that calibre, and most gunshops will not sell to you on your temporary import permit. Our firearms licencing is quite a process.