Heard Islands is a pretty small market, and I can tell you that the vast majority of Aussies aren't even aware that it exists.
You'd have to do some serious SEO work to get it rank in the non geo-specific version of the major search engines, and it probably wouldn't rank in the .com.au versions either as it's technically in the excise zone and note counted as part of the country.
Sorry to say it, but I think you're best bet is to stick with Adsense