I personally love shopping on ebay and gumtree, its where I got a vast majority of my stuff so would encourage you to check them out.
Another good place is forums themselves, posting ads looking to buy or purchasing other members plants - just gotta ensure they from AU.
Aquagreen also meant tI be a good store, but never purchased from them yet.
Sometimes LFS also has good deals on plants for sale, however its important to know what your buying as sometimes they sell non aquatic plants as well... and their stock is limited, expensive at times and rather low quality... But I have had success with them from time to time.
If you live in WA or NT, ensure you don't purchase plants from other states as they have quarantine laws and will be confiscated. Likewise, TAS can be a bit strict in plants coming in, and in others like NSW I believe Amazin frogbit is illegal to keep/sell (so ensure the plant you get is legal. if in doubt, ask!)
Hey Dude - wondering if I could get some advice from you (being the plant man ).
Setting up a 300l tank, nearly finished cycle with plants and fish. What I am interested in - in my area there are silver gum trees and some branches have interesting twists and turns.
Can I use these branches and will I have to soak them for about a year before I can use them.