A wedge is a wedge. It just needs to elevate your telescope to the correct angle, north or south. In the southern hemisphere you have it rotated such that it's angled towards the south pole, in the northern hemisphere you have it rotated such that it's angled to the northern pole. Easy
So, one wedge fits all.
The only situation where you need to worry is if you're at extreme latitudes, like very far south or very far north (which you're not, if you're in Sydney). Different wedges have different ranges of operation with respect to what latitude they can handle.
Roger.