You may find it hard to find a KE20 door in western australia, BUT it would be possible..
Places to find them would be simply in the quokka and every now and then a KE20 pops up in Pick A Part.
Other parts you could 'steal' off other model cars...
I don't know what your planning on paying for it, but a pretty good example of a KE20 was recently on TPC for $1000, which seemed reasonable to me...
Let us know whats happening with it...
And, by the way, I don't think I've already said it, but Welcome to Rollaclub!