I usually get my Logitech products through Frontosa - but I think you need to be registered with them? Not sure where else you could try.
Current pricing seems to be:
SP-LZ5500 - Logitech 970115 Z-5500 Digital, 5.1, Dolby Digital Pro Logicii, DTS® 96/24, THX; Digital SoundTouch Control Center with backlit Lcd, digital audio with Spdif (optical/coax), 5.1 channel, 505W (188+4x62+69) @ R2,653 + VAT
They also seem to have the Z-4540 listed - the one with the wireless rear speakers and 315W - R2,178 + VAT