Indian-style chick pea flour is actually made from chana dal, a smaller darker skinned cousin (not being politically correct here!) of the chickpea, and not from actual chickpeas.
So sometimes there is some confusion due to the alternative names for chickpea flour. It is also called chana flour, chana dal flour, gram flour, dal flour, gram dal flour, pea flour and besan flour. You may find it at that same store under any of those names.
Otherwise any Indian store in Sydney will definitely have it, under any of the above name, but most commonly as besan flour (pronounced similar to Ďbasiní, as in sink).
Actual chickpea flour (made from actual chickpeas) is popular in Italian cuisine and so is available from well-stocked Italian shops and goes by the name farina di ceci.
Plain flour would work as a substitute, in fact many flours would work, but they will certainly not yield the unique nutty depth of flavour that chick peas flour gives.
Thanks to www.kurma.net for answering this one.