The Bureau of Heraldry which is located together with the National Archives in Hamilton Street, Pretoria is the unit that can assist. A Coat of Arms is developed for a town, city, province or country. The Bureau of Heraldry has documented the Coats of Arms for most of the places in South Africa. They would therefore advise you as to whether the symbols you wish to use have been used by another entity or not. You would also have to register the Coat of Arms with the Bureau of Heraldry once it is completed.