Hey dude !
Like Duddles said, theres a fast50 track at appin motocross track, but its only open half the time which can be a pain in the backside, thats in south west sydney just between campbelltown and wollongong, i go out there a fair bit, and i also take my bikes to camden BMX track, its illegal but good fun, also in camden theres some pretty wicked bmx trails thats always Fun to hit up.
i live in South west sydney, hit me up threw email or msn if you want to meet up and i can show you a few places me and the local boys ride at.
we-ride-minis@live.com
Cheers !