Discussions of CTO's in other threads usually leads to the conclusion that they are not desirable and usually equivalent to a nice used stamp. However, Australia (and some other countries) issued CTO's that are now quite collectible. I've been scanning auction and selling sites lately and have found some nicer ones.
The Australian Kangaroos were issued for UPU distribution, but also in Specimen Sets. The Australian Commonwealth Specialist's Catalogue (ACSC) implies that these were available with a Melbourne postmark and also a Brisbane version. This is probably Melbourne, but since you only see a quarter of the cancel, we just have to guess. Scott 122, ACSC 29w.
Moving on to King George V, ACSC notes Melbourne CTO cancels along with Brisbane. I present two others. The first is 3 pence, Scott 72, ACSC 107w. I believe it is a CTO due to the quality of the cancel, however it is Sydney, so I'm now not sure.
Lastly, we have 4 pence, Scott 73, ACSC 116w. This one has a very clear cancel, Melbourne.
I'll post others later. Please join in if you have some to show.