If it’s the MS Website saying it’s not available, then I would try sending some furious emails to the customer service of MS and the computer manufacturer. You paid for a product, and they now refuse to deliver. Put the onus on them to find a way to deliver that product to you. Make a few veiled threats that you will publish your story on a techblog and call a lawyer, and I will bet they get you W7, somehow, free of charge.
I'm the type, when a company informs me of something such as MS did, to apologize for asking.
I need to rethink my approach with MS and demand to be given what I paid for and was promised!