I've never seen a non-9mm SP101 with a factory moon clip cut, but maybe I'm uninformed...
If it's a .38/.357: Unless you've had it modified, you're out of luck anyway, as a moon clipped cartridge won't allow the cylinder to close... You'd have to have it cut for the clips by a gunsmith, like this:
http://www.pinnacle-guns.com/revolver.asp
If it is a 9mm, midway has clips:
http://www.midwayusa.com/Product/593950/ranch-full-moon-clip-9mm-luger-5-round-blue-package-of-8
If it is a .38/.357, just beware: the moon clip groove is pretty narrow on revolver rounds, which doesn't allow for very thick clip material. They're nowhere near as strong as 9mm or .45 ACP moon clips. Consequentially, you need a good way to hold your reloads, because if you bend your moon clip, there's a high probability that you'll lock your revolver up good and tight, which is counterproductive to a defensive situation.
So, if you're looking to have the modification done....The More You Know (TM)