If you can't find molasses, you can substitute an equal amount of dark corn syrup, or use dark brown sugar (3/4 cup per cup of molasses).

Here's a reference page for a variety of liquid sweeteners. Hopefully you can find a good match that's available for you.
http://www.foodsubs.com...
(Merrill's substitution is good, but judging from your question and another one recently from Europe, the key is local availability. This site should help you with other ingredients, similar issues.)

I also live in Australia, and you can usually find blackstrap molasses in Coles in the health food section, or in Woolies in the honey section. If you do find it, I would recommend using half of the molasses called for in the recipe and adding the remaining quantity in golden syrup. If you are unable to find molasses at all, then simply use equal parts black treacle and golden syrup for the quantity called for in the recipe.