Where change money for good rates?

Where can one change money against good rates?

With the national change offices and banks, usually one gets a bad exchange rate. So i know of this exchange office in Amsterdam (Lorentz Exchange) where I got a commission free rate very close to the actual value of the Dollar.
I know you can also change at borders, but i want to have dollars, which isnt an official currency in Southern Africa.

For me i will be crossing Gauteng (pretoria) and Mpumalanga, so any tips will be welcome




but perhaps shops in other provinces can be of use for others, so dont hold back