I'm not sure if this will help you much. I came across this document from the web at saisc.co.za. This appears to be South African Institute of Steel Construction. A comment on this document casually says "Where structural steel is used, it is currently standard practice in South Africa to use Gr 300WA steel or Gr 350WA steel." I can't verify this, but this may be a starting place for you. It looks like they use a grade 300 steel as the low end.