There are loads of places to be honest, scattered right throughout Sydney - basically any public courts near the city will have people playing, Central courts are a good one, as are the ones near the SCG, and there's an outdoor court next to Broadway shopping centre (right next to the Peter Forsyth Auditorium). Out west though if you go to any local stadium there will probably be groups of guys booking out courts on Saturdays/Sundays that will be happy to have an extra body - I know Kevin Betts out at Mount Druitt has a group that plays Saturday mornings, but with school holidays and things it might be a little tougher than usual to find games.