jimmy,
you can check the links to the local clubs below:
st ives
http://www.stivesrccc.com
castle hill
http://www.hillsoffroadrc.com
ryde
http://www.sydneyrc.com
they are all within 30 mins drive from collaroy, the furthest being Castle Hill (i reckon). all within suburban area.
all 3 clubs organise fortnightly club racing, on sundays.