Firstly, welcome aboard. Great place for Multitool and SAK info.
You need a Craftsman 45517 kit (AFAIK Kershaw never sold a kit). These aren't very common these days, but they do turn up on US ebay occasionally. I'm guessing the file is corroded ? (this is extremely common).
babola: "Enjoy your tools and don't be afraid to air your opinion and feelings here, but do it in courteous and respectable way toward others, of course."