The answer to this question will depend on the type of license you have. In summary;
- OEM Windows: Nowhere!
- Retail Windows (physical): Nowhere!
- Retail Windows (digital download): Microsoft Store affiliate; Digital
Microsoft Store, digital download
As far as consumers go, Digital River and Microsoft Store is the only place you can legally download your purchesed copy of Windows. But you must have purchased it there to be able to download there. You should have an email witha a special download-link (unless you have deleted it already from inbox). These links seem to be valid indefinitely (so much so that they have began to spread throughout various blogs). Business and enterprise users, and Windows developers have other arrangements.
MSDN, MSDNAA, DreamSpark Premium
If you have a pre-activated OEM license you can use should be able to use an MSDN Windows image. But these are only available to people who have access to the TechNet Subscriber Downloads or MSDN Subscriber Downloads. Members of MSDN Academic Alliance (now called DreamSpark and DreamSpark Premium) also have limited access (not all editions) to MSDN images for Windows. So if you are a student at a university in Sweden, check with your faculty, you might already have access to MSDN images without knowing it.
You might be able to download the MSDN image for Windows through other, unofficial sources. I won't mention any of them here, for obvious reasons. I call this the semi-legal way. If you have a license for your Microsoft software, I see no reason for Microsoft to sue you. If you decide to go this way, make sure you verify that your download is authentic. You can read all about it on the web, even on the official MSDN website.
You will need one of the following MSDN files.
The typo in the first name is on them (Microsoft). The word "with" fell off somehow.
Backorder from OEM
If you have the OEM license, and neighter legal nor the semi-legal options are available to you, then you should contact your OEM. Your OEM is usually your computer manufactorer. (If you custom built your own, then call yourself for tech support.) Contact their technical support and ask them to send you a disc with appropriate Windows version. They sometimes obide and do as they are told, and sometimes they refuse. This can be true for the same company, same manufacturer.
In my own experience I was able to get a copy of Windows from HP for one computer model, but not the other. This seems to depend on who you talk to on their tech support team, which is rather stupid really, they should stay consistent and stick to their policy (whatever that is). Another reason for refusal to supply your Windows discs can also be because they ran out of them, they don't have them anymore. This is especially true in case of obsolete, no longer supported Windows versions.
Backorder from Microsoft Direct Services
If you have purchased the physical Retail product with license, a.k.a. FPP (Full Product Package) then you are the responsibility of Microsoft. You need to get through to Microsoft Direct Services. If you call the tech support, they can forward you to them. Just explain your case. You will have to provide your product key and for a small cahrge (for shipping, handling and pressing the discs) you will receive "Replacement Media" in a padded envelope.