South Africa's IMAX website is kak. There are no numbers to call. But help is at hand.
If you live in the Johannesburg or Pretoria area, your best bet is Menlyn. Cnr Atterbury Road & Louis Ave, Menlo Park, Pretoria.
Call: (012) 368 1188 to book.
I have just called and for today there is just one ticket left, and it's a front seat for the 9pm show. I guess I'll be going during the course of the week then...
The schedule for screen 1 is as follows:
12:00 15:00 18:00 21:00 every day, but no 21:00 show on Mondays.