Some online shops (US-based) do ship internationally, and others won't. It is extra work to ship internationally as there are Customs forms to be filled out.
If you do decide to order from overseas, be sure to check out the detail regarding shipping. Though most international packages do get delivered promptly, delays and lost packages sometimes do happen. You want to be sure that there is some sort of insurance available or included, in the unlikely event that a package gets lost.
Being in Australia, when it comes to ordering from out of the country, you're much luckier than if you were in the UK! I believe that Australia does not charge any import taxes/fees unless you're importing more than $500. (At least, that is what I was told several years back from one of our repeat customers in Australia.) In the UK, they charge a handling fee, PLUS taxes... and even the shipping fees are taxed. (Now that seems pretty heartless!)
I'm wondering if the prices you pay for fabric in Australia vary depending on the exchange rate? I've occasionally gone onto Australian quilt-fabric websites, but not often enough that I can get a sense of how the prices change depending on the relative strength of your currency.