Garmin maps can be found
here.
As for the others - they aren`t sold in Japan, so I imagine there is some sort of licensing issue. Pretty much all the maps used for navigation in Japan (including the Garmin one) are made by Zenrin. For companies that do not sell in Japan and do not often have their devices used in Japan (due to the difficulty of bringing a foreign car to the country), I imagine that the costs of licensing or producing a map independently would simply be too high.
You will most likely be much better off buying a small inexpensive unit in Japan - there are tons to choose from. It will also likely be in the same price range as purchasing maps of the country. The Garmin maps are 15,000yen and up. You can buy the absolute cheapest models of GPS for about that. (Although quality would obviously suffer tremendously.)
You may find it easiest to do something like you want to by buying a Garmin in Japan - already loaded with the Japanese maps - and purchase additional maps for locations outside of Japan. Garmin is considered one of the cheapy crappy GPS makers, and do not sell well in Japan, so are quite inexpensive. (Hi-res, 3D maps are the norm these days here.)