Square Enix has released their latest results briefing for the six month period of April-September 2012, which includes sale numbers of games released throughout Japan, North America, and Europe. Detailed on page six of the report is the amount of units shipped for each of their latest games, which shows that KINGDOM HEARTS 3D [Dream Drop Distance] has shipped 650,000 units across North America and Europe since its late-July 2012 release.
Note that shippment only means how much of the game was stocked and does not reflect actual unit sales.
Source: Gematsu