In general all US built aircraft before around 1974 had airspeed indicators in MPH. In the mid 1970's GAMA (General Aviation Manufacturing Association) recommended all manufacturers standardize on knots and so most but not all switched (Maule for example still to this day uses MPH calibrated airspeeed indicators). Unless the Australia CAA mandated all Aus registered aircraft have airspeed indicators in knots, there should be plenty of older aircraft still flying with their original MPH airspeed indicators, there certainly are in Canada, including my 1974 Grumman AA1B. I have no idea what the situation is in Europe.