Citi upgrade, page-17

Niu,
I understand to short on the ASX you either sell down you existing long position or you borrow and sell someone else's long position (and repay later with buys). Therefore offshore exchanges and hedges aren't relevant to the these ASX settlement obligations. You need to open or have borrowed an Australian-based holding to short a stock.
Who in Australia offers these substantial holdings to short traders? Top 20 holders? A broker (market maker) who may have a substantial holding? Custodians of fund managers / major holders?