As far as I know we don't have many dealers of high repute who deal with international collectables.
Leski auctuon group in Melbourne deal or used to deal in signed memorabilia etc. The other is this group also located in Australia. I don't know anything about them. Just viewing them after your post. They do have a couple of interesting pieces allegedly signed by JFK and Elvis Presley. Both are highly priced.
Most of my collection mainly USA presidential signatures were obtained in the United States way back in the late 90's early 2000's.
I have only purchased two items locally. One being a signed David Carradine sword and a kill bill signed picture by David Carradine and Uma Thurman. Both of these have been posted previously.
Sorry I Steve it's not much help! I hope done other aussies may know more.