Um... you can try TREKNOLOGY BIKES at henry park, they cost about twice the price for a normal 6061 frame bike, but they come with disc brakes, those hydraulic ones... maybe BIKE HAUS somewhere on the out skirts of coronation... theres another bike haus at six avenue, somewhere near the seven eleven and the video EZ... and theres rodalink cycle near there too...
its some where off beauty world, about a couple hundred metres before, the left turn if you're driving... Best of all, buy GIANT XTC hardtails... Cheap, light, and durable...