Korg DS-10 synthesizer program comes out on November 4, you won't be able to purchase it just anywhere. GameStop, for one, doesn't care to stock a $40 DS non-game, apparently. In fact, the list of stores who are carrying the feature-rich synthesizer cartridge, as sent to 1UP by publisher XSEED, looks a bit paltry.
According to the list, only Amazon, Fry's, Micro Center, Best Buy, J&R, Game Crazy, and EB (in Canada) are planning to stock DS-10. Amazon, by the way, is taking preorders for $36.99. Also they bring games directly to your house, so maybe it isn't so problematic that more stores aren't carrying DS-10.