In CrossSearch, you can often filter your results by location, by selecting country or region names under Subject Terms in the left-hand column beside your search results. But this option isn't normally available for Australia, so you need to type Australia as one of your search words when you enter the search. eg, "green politics" Australia. (Quotation marks around green politics searches for those words next to each other).
Typing Australia* will find all words starting with Australia, such as Australia, Australians, Australian, Australiana.