If you have a Windows XP installation CD (at an earlier SP level of course), it is possible to create a new XP installation CD, slipstreaming SP3 into it. If you would like to do that, post back for instructions. That is the disk that you would need.
However, you can still run sfc without that CD as long as you have an i386 folder on your C: drive. If so, have a look at these pages for instructions:
Here's the deal. SFC/scannow is essentially useless. Yes, it's possible to use the slipstream process and create a bootable XP installation CD that will have SP3 integrated into it. And yes, it's possible to use this with a system at the SP3 level and
then run SFC/scannow.
It probably won't help you one bit!
If you have hung around this forum long enough, you will see a number of well-meaning people (often so-called MIicrosoft Support Engineers!) suggest that users run SFC. But it's almost always the wrong advice. Even if a person can figure out how to jump
through all the hoops to make it work, it probably won't solve the problem the user is having.
That being said, assuming you're the curious type...
If you wish to run SFC/scannow, the SP levels need to match. So if you have Windows XP installed on your hard drive and it has been updated to the SP3 level and you wish to run SFC, you better have a Windows XP installation CD that is at the SP3 level.
Yes, it is possible to copy the i386 folder from that CD onto some location on your hard drive (usually C:\i386) and alter a registry setting: