Winton typically run them 2 or 3 times a year.
Previously, you'd sign up for a single day AASA license, have an acceptable helmet (they may check that it is within date or for a current SNELL approval, depending on the day), remove all loose objects and you're good.
Winton calendar is here -
http://www.wintonraceway.com.au/calendar
'Fun day' means no official timing and drive within your limits.
