Google hasn’t officially offered the Chromecast outside the U.S., but Amazon is now shipping internationally. There has been reports that Amazon will ship to areas such as the UK, Australia, Germany, Hong Kong, and Canada. There are probably more areas so give it a shot now.
There is only one caveat: you will need the Chromecast app in order to setup your shiny new Chromecast. Unfortunately, it’s only available in the U.S. Play Store, but you can probably find the APK with a quick Google Search or you can use something like TunnelBear VPN to give yourself a U.S. IP address when accessing the Play Store.