Which supplier? Since your in Gauteng I would suggest trying Cyberdyne systems their pricelist indicates only a shortage of 2 3.5" Drives 400Gb RAID EDITION & 500Gb both from Western Digital.
Also their prices are quite good in my opinion and their service levels are probably the best in the industry (bold statement yes but I stand by it )
I haven't experienced any HDD shortage yet - I get from DCC, Eurobyte, Rectron, Frontosa, etc - depends on what the client wants/needs... who are you getting from antowan?