Looking for a 5900x myself, came across the site Overclockers UK has plenty of 5800x
Note that despite the listing price of £379.99, adding 5800x to the basket and select Australia as a destination, the final price is £344 (including DHL shipping) (A $624.20).
Goods total £316.66*
Delivery costs £27.57*
Total order value £344.23
They also have 5600x in stock but not shipping to Australia for some reason.
I didn't pull the trigger myself but if someone gets one successfully, please let me know.
Update: It's even cheaper now. Down from A$624.2 to ~A$606 depending on the exchange rate of your payment.