I ran into this issue myself. If you are like me - in the U.S. NW - you will need to purchase the license key(s) at a Microsoft or authorized store. I found that the Pro pack is available for order through places like Amazon, but the WMC pack that I want seems to only be available through the (physical) Microsoft store. Thanks Microsoft...
The information that N.Scott.Pearson provided you is correct, you can confirm that here: