Welcome Chris, I have used most of the suppliers in Australia at one time and another so here is a annotated list:
http://retrosound.com.au Greg is good for mainly Fender bits, tweed & tolex, Mercury Magnetics trannies, cabinet hardware, BBQ Speakers and Celestion. They also build cabinets but as Daz says they are a bit on the expensive side.
http://directcomponents.biz Kevin has tubes, caps, wire, reverb tanks he is also an importer of Sprague and Mica caps. Ask if you don't see what you want as he only has a small percentage in his online catalogue.
http://evatco.com.au Arthur has a great selection of tubes and stocks Sprague caps, Jensen speakers, Hammond trannies and chassis etc.
http://blankguitarsandamps.com.au Tommy does Sammi speakers (so do I) he can also sell you tolex etc.
I use the normal outlets like RS components, Jaycar, Altronics and Dick Smith for resistors, caps, hook up wire and odds and sods. Altronics do a good selection of 1Watt resistors.
Nic at Ceritone quoted some good prices on Trannies and they are the most problematic components to source around here, Kevin is looking at getting some wound so approach him.
I get blank chassis made to size locally and they work out cheaper than the Hammond equivalents.
Visit the web sites and have a browse. RS components have an online catalogue search but it takes me ages to find what I am looking for.
Anything you can't find let me know and I will see if I can help.
Good Luck
Nigel