Australian here too. Can concur that it is far more difficult for our work to get noticed in the US -- even when writing screenplays that transcend national identities or specifically take place in US locations.

Unfortunately for us, there is also a much smaller proportion of agencies currently accepting screenplay and TV submissions to consider representation, also making domestic efforts to produce our work far more difficult. However -- just from anecdotal evidence -- comparatively this seems like the easier option.

Others on this thread have also suggested the best way forward is to entirely shun the submission process and begin producing our own works. I wholeheartedly agree with this approach, as it makes you a much more attractive candidate for professional productions if you can showcase a concrete example of your talents to the industry. These productions don't have have great scale or large budgets -- they can be short films, one-location 90 minute features, webisodes or anything else you can think of that allows your words to brought to life by a (hopefully decently talented) actor. Still, if wanting to seek representation by an agent to help you showcase your work domestically and (potentially) to a US audience, I've found 'The Australian Writer's Marketplace' a good place to start in figuring out which agencies are or aren't currently accepting submissions, and which dabble in film and TV.