Ask Cheapy. He did comment in a forum that the DS lites are still hard to find in Japan. You choose the worst time to try and get one I think.
The launch of "The New Super Mario Bros" game probably sold out all the stock in all the stores. NSMB sold just under 900,00 copies in it's first week...crazy. Look at DS lites sales this week too. 285,000. That's almost double last week. Coincidence? I think not.
Soooo...good luck!