In Melbourne, the main shops where you can obtain caving/climbing gear are –
The Wilderness Shop
There are also mail-order outlets, Australian and overseas. Aspiring in NZ is good for suits and packs. Google will find them all.
In terms of which brand/model, I suggest –
Petzl SuperAvanti harness
Petzl Ascension hand ascender
Petzl Croll chest ascender
SRTE Stop Descender (Petzl Stop is alternative)
Aspiring Trog Suit (but actually cotton overalls, from Rivers Clearance Shop or elsewhere, are adequate in Victoria)
Aspiring cave pack
Roca Espeleo 9mm rope
Any CE-marked screw-gate aluminium karabiners
Also, I suggest you buy (or borrow and read) the book Alpine Caving Techniques.