It's really easy to make your own. You can either make your own sponge cake or if you want quick and easy, just buy a rectangular sponge cake from your local Spar bakery...keeps for about a week I think. And if you keep icing sugar, cocoa powder and dessicated coconut on hand, you can have lamingtons whenever you want to. For the icing, you will need...
500g icing sugar
pinch salt
90ml cocoa powder
30ml soft margarine
boiling water
dessicated coconut
Mix icing sugar ,salt and cocoa and sift it to remove lumps. Add to margarine and mix well. Pour in enough boiling water to make a runny icing.
Cut cake into strips about 3cm wide. Cut each strip across into squares. Place coconut in a dish.
Dip cake pieces in icing, then toss in coconut...voila!...lamingtons.
I normally use the entire cake when I make it, so you might want to adjust the quantities for the icing mixture if you're making less. You might also want to adjust the cocoa amount, depending on whether you like that slightly bitter chocolate taste or not.