The simplest shims to use are feeler guages. Go to supercheap and buy a set of feeler guages for less than $10. These are made of stainless though and won't bend very easily.
If the local Bunnings idea doesn't pan out, I am sure I can lay my hands on some of the "500mph" stuff. Or the other fly-boys here could, Flasher or the likes.
Sing out if you need it.
Gary