A new wave of Chrome OS devices, including the first Chrome OS desktop and revamped Chromebook hardware, were launched today. While Google's announcement mentions that the Samsung machines will be available outside the US and UK in "other select countries over the coming weeks", unfortunately Australia isn't on that list.
A Google Australia spokesperson told Lifehacker this morning that there was "nothing to announce for Australia at this stage". Google has quite a track record of not releasing products in Australia, so this isn't altogether surprising. If you're keen to experience Chrome OS, you can build your own Chromebook using Chromium, but that's hardly representative of the no-hassle experience Chromebooks (and now Chromeboxes) are meant to represent.