I have a 6mm Musgrave on a large martini action. Is PMP 6mm Musgrave ammo or brass still available in South Africa?

Sadly, no. PMP itself is no more, either. It was managed into the ground by the current South African government (it was a state-owned enterprise) and closed its doors a few years ago.

By the end, PMP's quality was so bad that practically nobody bothered with their stuff in any event.