You're going to struggle to find year on year data regarding unit sales of skis, let alone a concise break down on the sales of specific categories of skis.
If you can somehow get hold of an analyst's report on a company that owns a ski manufacturer, e.g. Amer sports which owns the likes of Salomon and Atomic (who in turn make skis for other companies like Armada) then you'll be set.
However, these reports are hard to come by. If you've got the time and are prepared to tough it out then you might want to try a focused search using Baidu, China's version of Google. Baidu seems a lot less fussed about intellectual property rights and will occasionally give you access to locally hosted copies of such reports...for free (definitely a plus unless you've got a few grand or more burning a hole in your pocket).
Otherwise...I seem to remember reading an article including a lot of data supplied by someone at Atomic. From memory, it has global ski and snowboard sales for a few seasons, the relative proportion of ski and snowboard sales by continent and the season when twin tip ski over took all other types of ski in retail sales in the US (2007 if my memory serves me correctly).