As of June 2015 it is still possible to purchase Windows 7 keys through retailers such as Fry's Electronics. Microsoft has stopped issuing new keys to retailers, but it is legal for existing stock to continue to be sold.
It is also possible to purchase keys secondhand from private sellers through sites such as Amazon and eBay.
Microsoft ceased issuing new Windows 7 keys as of October 31, 2014. Licenses for OEMs to include most versions of Windows 7 on their PCs will end on October 31, 2015. Windows 7 Professional is a possible exception to this, as Microsoft has yet to establish an end sale date for it.