TWRoO on 19 November 2008
This is an article vaio posted here on VGC, which has the 2.4 million figure in..... not exactly directly from Nintendo but it's a start.
http://www.vgchartz.com/forum/thread.php?id=34836
Los Angeles Times:
http://www.latimes.com/technology/la-fi-nintendo27-2008oct27,0,6221366.story
(it's part way down, though there is a misquote there saying last year it was at 1.6 million... but the evidence is on the page to work out it's a mistake because it also says "33% increase" which only works with 1.8 to 2.4 million)
