Among other shops, off the top of my head Port Melbourne Cycles handle Pinarello and Bike Force (near IKEA Richmond, for example) carry Orbea, but I dunno if either shop does second-hand. They might be useful to ask.
thanks guys. yeah I tried Port Melbs but they've stopped supplying the 2nd hand bikes, same with bike force. I'll check out the bicycle recycle. I might have to bite the bullet and buy brand new!