Lots of the bridal websites have sections for bridesmaid dresses, you could have a look on there and get an idea of what you like, then you could go to a dressmaker to make something similar and tailored to you! That is what I did for my wedding and for other peoples weddings that I have been bridesmaid for. I also would try DJ's, Myer and shops like Green with Envy - they often have gorgeous stuff. The wedding I was in last year we found our silk dresses at Sportsgirl of all places!