I'm an Auslan interpreter. I think it's great that people are interested in learning Auslan as a second language!
There are short community courses run one day a week for a term at different places in Sydney. There are also the proper certificates 2,3 and 4 and the diploma by the Deaf Society of NSW. I used to do a bit of teaching with them. And then there is TAFE, probably only Blacktown and North Sydney still.
It helps heaps when you are learning to get in with deafies and sign regularly. Try the deaf clubs once a month at Burwood and Parramatta. There are also some auslan student groups that pop up sporadically. Deaf churches, mostly pentecostal or catholic or JW, if you are so inclined.
IMHO, if you get using the language to communicate, that helps heaps. It's also helpful if you can decouple signing from speaking, that way it's easier to learn to sign naturally, rather than signing in english word order.
I have nothing to do w Makaton, but I think they have recently changed their name to Key Signing Australia or some such. It's a simplified system of signing the important words in simple spoken English sentences to help kids with intellectual impairment etc to understand, so the name change makes sense. They originally borrowed signs from British Sign Language, then changed over to Auslan signs.
Auslan - Signbank is a good dictionary, but as w any dictionary, it can't show you the language in action. There are some interesting clips on youtube, but there are many more in American Sign Language, but if you search for Auslan you'll find a few.