Have you tried calling every TRU in the Sydney metropolitan area? Because that's what I did when I was after MP Optimus Prime until I finally found a TRU that had one in stock, then got them to reserve the toy for me. If that doesn't work, call TRU head office and ask them to source one for you.
P.S.:
Gofigure is selling an MP Wheeljack at <AU RRP here 