you can actually use a forwarding service in the US that will forward your goods bought online or wherever in the US to Sydney. its pretty much a fee to "rent" an address and forward it to your real address.
I'm not sure what their names are, but I'm sure if you search the forum, you'll find that a lot of people use these services.
What about the British sites like brownsfashion.com, matchesfashion.com, harveynichols.com? Or other international sites like mytheresa.com or luisaviaroma.com? Some of them don't have too many YSL bags right now because the sales are just ending, but they are restocking for spring.
I'm from Sydney and I could never find anything. I went to DJs when I was back in Sydney around Christmas to scope out their YSL collection and it was worse than dismal. They had one clutch and one Muse in their entire locked up glass case...
I also suggest calling the YSL boutiques since they're having a sale on right now too around the world. Their numbers are listed on their website and I'm sure the deal with international orders. I'm in teh US right now and I've bought from boutiques in Europe when they didn't have the style in the US.