I had this same question and eventually found the answer.

The image file needed is X17-48538.img available from the Microsoft OEM site.

It contains:

  1. readme.txt 2/26/2011 1204
  2. windows6.1-KB976902-X86-Wave0.cab 2/26/2011 4532924
  3. windows6.1-KB976902-X86-Wave1.cab 2/26/2011 4531728
  4. windows6.1-KB976932-X86-Wave0.cab 2/26/2011 354704066
  5. windows6.1-KB976932-X86-Wave1.cab 2/26/2011 541001258

You should be able to get it through your OEM if you don't have direct access to the MyOEM site.