Kirsty, I have a womens weekly kids cake book, it's the fantastic cakes with a lion on the front. Anyway, in the back of it, they have an aussie flag cake.
They've made it from a 26cm x 36cm sized baking dish, covered it with whipped cream instead of an icing, then decorated it with blueberries and strawberries. The blueberries - 1.5kgs of them cover pretty much cover most of the cake for the blue, and strawberries for the red', then melted white chocolate piped into star shapes and let to set for the southern cross. it looks pretty cool. If you want I can try to scan it tonight and email it too you?

Nic