Hi there,
Because of the nature of bisexuality (and it's common acceptance in the straight scene), there is no ONE place to go to, to find bisexual women/people to pick-up.
Best area of Sydney I'd say, is Newtown (approx 15mins from Sydney CBD) and the surrounding suburbs, such as Erskineville, Enmore & Petersham. The Imperial Hotel in Erskineville is usually a great place for queers (of all walks) to hang out, as well Zanzibar in Newtown, or any other pub in the north part of King St, Newtown.
Hope this helps, and best of luck ;-)
SydBiMan