Wander down to any club and ask around, letting them know you're experienced. The sailing office may have a crew list but get out and ask and you'll have more luck.

A few of the twilights are;

Monday - RMYC Pittwater
Tuesday - Drummoyne?
Wednesday - CYCA
Thursday - Middle Harbour YC
Friday - Balmain; RSYS?

49ers only sail from Woollahra SC, and the fleet is small. The B14 fleet is another option; also at Woollahra, also small.

You could be better off trying a 16 Foot Skiff at Middle Harbour or Manly 16 Foot Skiff clubs.

Best option may be to get on a Historical Skiff through the Sydney Flying Squadron. They are nothing like a 9er but they are great, and you may pick up skiff cred and contacts pretty easily as AFAIK they are often looking for crew.