There are not many in Australia, and just a few in Sydney, 1 in Adelaide, and can't comment on Melbourne but I know there are some.
Corlection - http://www.corlection.com/
In the city on Pitt street near Central station and prob ur best option for Japanese brands. They carry a nice range: Momotaro, Japan Blue, Strike Gold, PBJ, Levis, Kaw
atako, Red Wings, Thorogood. Really pleasant guys who run the shop.
Halfsleeve - http://halfsleeve.net/
Just popped in there once, seem to be the only place I know of that carry Imperial.
Incu - http://www.incuclothing.com/content/home/
Two locations, one on Oxford Street in Paddington, one in the QVB. Both carry APCs.
Harrolds - http://harrolds.com.au/
A bit strange, they carry high end couture and you wouldnt expect to be buying ur raws here (not much streetwear going on here) but they seem to have giant stockpile of Naked and Famous. Prices are a inflated (just like everything else here in Oz)
Nudies....The Nudie store in Paddington, General Pants, David Jones. Not hard to find.
There was a guy who used to do it, not sure if he still does:http://mikhailzenon.com/blog/
Otherwise you probably have to send to these guys in Adelaide:
Right Hand Distribution - http://www.righthanddistribution.com/
Some Momotaro, Samurai, Flathead, Tellason, Sugarcane, Nudie. Very very helpful staff and always happy to chat denim. They offer chainstitching service as well.
If anyone has any other hidden gems, please post.