You need to locate fertilizer base stock material which available to you in South Africa. ... See this refference for how to calculate fertilizer formations and base fertilizers to use in the blends. ref:
https://www.google.com/url?sa=t&rct=...LVona4Cnu8W6BT
Also, this reference gives basic blend formulas & amounts. ref:
https://www.google.com/url?sa=t&rct=...COk70FlcsPBKVp
Both above reference list fertilizer stock materials needed or to use in making a blend formulation. ... Don't forget the micro elements needed! ... And, be careful using urea as it is not comparable with some fertilizer types.
The second reference shown above using 7 basic fertilizers (raw materials) gives the many different blends that can be formulated and the weight of each base fertilizer required.