It may be harder to find, but if you can get hold of an artificial fabric like Cordura, it has several advantages - ie. it doesn't soak up water, like a cotton based fabric will, and it is probably more abrasion-resistant. Your best bet will probably be finding an internet store that will deliver to your area (Australia?), since I have yet to see a local haberdashery that carries cordura, gore-tex or any other artificial fabric (well, I've seen rip-stop nylon, but not of a quality tough enough for a bike bag..)