Q: Who can I obtain a bursary from, other than my university (South Africa), if I am studying to pursue a career in Physics, Astronomy or Astrophysics?
A: If you are studying for a Postgraduate degree you should consider contacting the National Research Foundation. They offer funding in the form of bursaries and scholarships to most areas of study. You can visit their website at: http://www.nrf.ac.za 
The FirstStep website also provides a list of many different bursaries and scholarships available to South African students. You may qualify for a bursary without even knowing so be sure to check it out by viewing the Finance section of the website!

A simple Google search will enable you to find a whole host of bursaries offered in the field you are interested in. For example, the South African Weather Service offers a limited amount of bursaries to people wanting to become Meteorologists, which involves the study of Physics.
You may want to conduct a simple Google search of South African websites to find out which companies or organisations offer such bursaries that affect you.