First up, stop advertising every time you write a message. You're not allowed to advertise your products on the forum and it is frowned upon by other members.
You can list on any site you like. You will be paid in their currency though. If you list on the US site, you'll advertise in USD and paid in USD. You then have to pay the conversion rate either through PayPal or through your bank to convert it into AUD. Why not just have your listings set to worldwide, excluding countries you don't want to post to. If someone in America or UK does a search on their own site for your type of product, it will come up in their search results.
