You need a valid Visa in order to do this. This might be a work, business or even student Visa but if you are not a South African citizen you will need this. Secondly you have to go to South Africa and open the Account in person as due to money laundering countries it's hard to do these things online.
One work around is to find an agent and open an offshore company and account in South Africa (some agents charge around $500) and charge more to open the account. Another work around would be to find a resident to partner with and form a company and give them non controlling stake and open a business account. This requires you to be in SA again.