On Japanese Mitsubishi Pajero imports there was a box called a frequency expander that you could buy, it was wired into the power feeds of the audio system and then the aerial was fed through it. This allowed the factory fitted radio to give the full UK FM frequency range.
Usually the importer would sort this out along with any other quirks that were needed to meet the laws of the country that was importing the car, such as a rear fog light with an illuminated switch, which is a requirement in the UK but not in Japan.