Giles, fellow Pom here (although I try to keep it to myself), been around Sydney for 3.5 years and have windsurfed the whole time (bought kit within 1 week of arriving!). I managed to meet some locals in the northern beaches but the best thing I found for meeting really passionate windsurfers (who are also good blokes) was to join the NSW Wavesailing Association.
You get to find new beaches (one thing I find odd here is that you get to an awesome beach with awesome waves and no one is out... I start thinking of Noah's), meet lots of people and ultimately improve massively as the standard is pretty damn good compared to my old local beaches.
You made an excellent choice