It seems a lot of stores have been ordering small quantities, selling out quickly, then continuing to only order small quantities. They expect strategy games to sell poorly, and don't bother changing their order quantities when they're proven wrong... and the game keeps selling out. This issue seems to be particularly bad in Canada. So if you want a retail copy, the best recommendation would be to find out *when* they're getting it in, and be there when it does.
The EB Games near me ordered only a few copies to start, but have ramped up their orders as they are constantly selling out of them. The problem here is that they are still only getting maybe 2 or 3 in each shipment.