The sizes of the t-shirts from Kung Fu are the same those from American Apparel, Kina. Here's links to their size vharts for
women and
men.
Like a few people have said, though, postage isn't cheap. You can find out exactly how much it is by adding the items you want to your cart, and then using the shipping estimator. As an example, depending on how fast you wanted it, a men's t-shirt would cost a minimum of US$10 and a maximum of US$30 to ship to Australia.
Okay, the prize for my helpfulness is that I get to be nosey: What are you thinking of buying?