There's not much stuff in Brisbane for the current M3, if you joined the BMW Club of Brisbane, free membership when you bought your M3, check with them, they also have a mag they send out every 3 months or try
http://www.southernbm.com.au/ in Melbourne. I have bought a bit of stuff off them, otherwise get the smaller mods items from the vendors on this forum from the States.
Most of my stuff comes the States, oh yes Hamann are now in Sydney (
www.ramspeed.com.au), the website is not complete yet.