Whether or not a stock is short sellable is determined by the...

Whether or not a stock is short sellable is determined by the ASX and as known as the "Short Sell Indicator".

There are currently 195 stocks that are short sellable.

The ASX list on their web site only shows those stocks of the 195 that have short positions currently open.

Short selling requires a full service broker (I don't know of any that do it online), introduces margin issues (usually a separate account), uptick rule for initiating a short position, requires stock to "borrow" to take the position and a lot more back office work at the broker to initiate.

Check out CFDs - they may your shorting life much easier.