The Amazon.com.au marketplace is scheduled to be launched in December of 2017. If you want to develop Amazon MWS applications for sellers in Australia, you can begin now. Here is some information and resources:
Amazon MWS portal
The Amazon MWS portal contains links to client libraries, documentation, developer support, the Amazon MWS Scratchpad, and other resources.
Endpoint and MarketplaceId
Here are the Amazon MWS endpoint for Australia and the Australia MarketplaceId:
For more information, see Amazon MWS endpoints and MarketplaceId values
The following Amazon MWS services are available in Australia today: