You could check out
http://www.vgchartz.com/. They have the latest figures for videogame sales. I've been checking the sales figures for the last month but Clod haven't even broken through top 30 (need to be a premium user to see the whole charts) which indicates rather low sales. I'm not surprised though since it is after all a very niche game and Russia/US are probably the main markets.
P.S Even though the sales might be weak right now I don't recall IL-2 selling millions of copies at launch either, it sells over time I reckon.