Just check out with an AMEX card and it shows the discount:
Items: USD 149.00
Shipping & handling: USD 10.01
AMEX Promotion: -USD 22.35
Total before tax: USD 136.66
Estimated tax to be collected: USD 0.00
You can checkout in USD and be charged the foreign exchange fee with your card holder or just pay by AUD on Amazon (~AU $193)
I can't find it advertised anywhere though. Seems significantly cheaper than anywhere in Aus and even more so if you are in the market for >1.
Haven't tried but also likely it applies to other sizes or more items!
Discount also works for 6TB drives $221USD or $313 AUD using Amazon AUD billing