Buy Original Windows 8 with Limited Time Promotional Offer
The link rich us at,
click here or copy paste the address http://windows.microsoft.com/en-US/windows/worldwide
For India this would as follows,
Select your region or country and go on home > Download & Shop > Buy Windows 8 > Click Button "Download Pro for INR 1999
After above step, you will given option to download small file named Windows8-UpgradeAssistant. Open that file and follow the instruction.