I have it installed I just need to activate it. Thanks guys. Not sure where this post belongs but you guys seem to know a lot about bootcamp.
EDIT!- Windows 8.1
I'm not 100% sure, but I don't think you can just buy a key; you need to buy a retail copy.
See FAQ from Microsoft here: http://windows.microsoft.com/en-gb/windows/get-windows-product-key#get-windows-product-key=windows-7
Have you tried activating your copy of Windows - does it give you some options to buy a key?
By the way, if it helps, you may want to seek answers to this in other Microsoft-related/specific forums/subreddits - Bootcamp has no relation to registering Windows.