Assuming you mean volume turnover, then the reason there is limited information available is because FX trading is global and cross border in nature.
Given most CB's require such turnover information be reported for statistical recording purposes the you can check the websites for the CB's and see the turnover by the banks under their supervision.
For Australia, go to the RBA website: http://www.rba.gov.au/Statistics/AlphaListing/alpha_listing_f.html and check out the Foreign Exchange Turnover stats.
However, given the stats are only submitted monthly then the numbers are always going to be a couple of months old.
