QUESTION :
I want to build a Win8 VM on my MBA, but can’t find anywhere to download this OS…
ANSWER :
There seems to be an article here that tells you how to get the ISO. The thing about this article is that you have to have a product key. Thus you aren’t able to get out of buying it.
Microsoft usually only sells “OEM System Builder” licences to vendors, in bulk; You basically can’t buy just one, and “general public” isn’t meant to buy them at all.
This licence also does not allow for installing on a VM.
You can buy a non-OEM licence and download the image directly from MS site.