THis is off the wall, but I know from experience that the AM radio frequencies in Australia (cannot speak for New Zealand) are set at a 9 kHz spread instead of the 10 kHz spread we use here in the states. My old Radio Shack portable shortwave radio had a button you could set to change the kHz spread on the AM band.

Maybe the factory presets are set to a spread of 10 rather than 9? But even so, one should be able to manually tune the dial and find what you're looking for. But then I've never seen a Prius' radio, just an HCH one.