Hatsune Miku: Project DIVA Mega 39s (known as Mega Mix in the West) seems to be a mega hit in Japan. Japanese retailer Yodobashi Camera has completely sold out of physical copies for the Vocaloid rhythm game, but luckily, back-orders are still being taken. Although the Sega published title is still available at other retailers in Japan, it wouldn't be surprising to see a stock shortage in the near future. As a Western release has been confirmed, hopefully we get a release date announcement soon, and stock is much more plentiful.
Make sure to grab a copy!