Hello Dan,
The Australias capability is relatively new and we regret any issues with it. We were able to reproduce the issue as you described it. Tell us, are you able to get the AUS search working at any point, for example, the first load of the page? This info would help us in troubleshooting.
As a workaround, you would have to cut and paste the item number directly from the eBay item page. You can grab it from the URL or the bottom-right corner of the item page.
Thanks and let us know.
bidslammer