I dragged a couple of threads out for you by searching for "reef island" where I have not yet sailed. These basically boil down to "the map looks like there should be somewhere but there itsn't anywhere so go to Inverloch.
www.seabreeze.com.au/forums/Windsurfing/Victoria/Avonsleigh-where-is-the-closest-sailing-spotwww.seabreeze.com.au/forums/Windsurfing/Victoria/spot-advice-needed-pleaseBut given that you say "beginner/intermediate" I read "If it all goes wrong I'd like to be blown back onto the beach".
If you can make the distance, you will probably have a great time at Inverloch, where there will be a heap of windsurfers, flat water and hopefully if the forecast for tomorrow is correct, it will get windy.