Prostitution is legal in Austria, so what there is available shouldn't be too hard to find - they have no reason to hide it under the counter so to speak. The brothels in Vienna suburbs are quite obvious as you walk past, for example. I suggest some basic Google searches, plus looking on the Vienna and similar threads for resources such as review sites and the like.
A word of warning that bareback seems to be almost the norm in Austria, most girls seem to offer it. Unfortunately it has recently been made illegal in Austria to advertise it, which complicates checking if a girl offers it or not. More info on the recent Vienna thread.