The 8X57 is very popular in Namibia (I'm told) and fairly so in South Africa. Certain dealers will carry ammo - Rosenthals in Windhoek, Namibia and in Cape Town, South Africa and possibly the Powder Keg in JHB should have. But you won't be spoilt for choice and it would be good to check in advance. I would suggest you take your own ammo anyway.
There are better calibers for the longer shots, but I'd happily carry an 8X57 for much of what I hunt.
I've always liked the 8X68 on paper - a great beltless magnum - never owned or shot one. But .30 and .33 bullet choice is just so much better. There isn't much out there for the reloader if it isn't popular in ther US. I always thought it was a good candidate for wildcatting to a .30! But brass is a limitation - probably RWS only (good brass though!)
Anyhow... that's a thread drift, so I'll leave it there.