I want to build a Win8 VM on my MBA, but can’t find anywhere to download this OS…
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.