AFAIK there's no way to convert/port a map from another format to tomtom one. Also, there are only a few maps of Japan for the most common navigation systems. I can only remember some maps for Garmin, like this one. You can find some other maps by searching in Garmin maps section.
I've read somewhere that it's possible to load raster maps in TomTom units using an unofficial extension, but probably this is not what you're looking for.