First of all, as long as you have your valid license number, any copy of Windows will do, so if you manage to obtain a copy from a friend or elsewhere (just don't buy it on eBay), it will suffice. Your second option is the repair disk that you can make from Windows 7, search the tutorial section for instructions, but this will not be a "re-installation disk", namely you won't be able to use it for a clean install.
The current logic is that you don't need the disk since there is a special Recovery Partition on your hard drive that can be used to restore the factory state of your system. Of course, that won't help if the drive burns out, but that's what they argue these days.
Hope this helps.