Hello peter and welcome to the forum!
It should not be a problem to register your unit at Humminbird's website even if your from down under. I got mine registered without problems on the site here in Germany.
One thing you have to do is when you register or create an account: Do NOT hit the "enter" key on your keyboard when you finished filling the boxes! Click on the "submit" or "add product" button on the website.
That's a glitch on HB's site.
Hope this helps.
Regards / Harry