Try
Shopbot for these items, they provide price comparison for online retailers. You deal direct with the on line retailers.
I had a look at the
Photobuff website I usually get my gear from but they dont seem to have it. perhaps a call to them might be worth your while. they are great and you can pick up if in Melbourne.
The Sigma 15mm EX fisheye is available from $580, and the 8mm fisheye for under $800.