Help!

I lost my disk for Office 2010 Professional Plus but still have my key.  When I upgraded to Win 8 I assumed that I would be able to download a copy as it had been available before, but now the website only shows the download for Office 2013 Professional Plus.  When I tried the "enter the key" website for downloading my version, it told me that this version is not available for free download.  This didn't seem right to me given its previous availability.

Thanks,

V