How they get it into Australia and New Zealand I'm not 100% sure but most of these goods are shipped as gift items (most probably why they are not intercepted) or smuggled into the country illegally otherwise they would have already been intercepted by Customs and destroyed. I've searched for an hour or so to find information that may say how this is being accomplished but however I found none - Which is what I expected anyway, no one would share their dirty little secrets online! :)
Australia has a particularly strong stand against counterfeit items, however due to the economy many of the low-middle class families will continue to fall prey to counterfeit products hence the the ever flourishing industry, the same is true even in the US. So long as there are people who will buy counterfeit items sellers will continue to find a way to source them and sell them.
I found this thread on the forum and its has a number of good posts with tips and info, in case you want to check it out here's the link - Link hidden: Login to view
Hope this helps, somehow :)