Try Monza Motors in Bayswater (9720 4442), or Milano Spares in Thomastown (9462 2138).  I had to get the same part a few years ago, and from memory (don't quote me on this) I think it was around  $120-140, but I could be very much mistaken with that price cos it was a while ago.  That's for a genuine Alfa part.

Let me know if you're not able to get one, i have a spare one lying around which won't pass a roadworthy because it doesn't self-cancel, but it will still , erm, indicate.