You could find the right sized clock key on eBay or elsewhere and use that if you can't find an original...
You can make one if you have some small brass or copper tubing.Grind a finishing nail to the correct size square then tap it into the pipe to form a square.Bend the other end for the turn end. Most clock keys are a bit too large but some do fit.You could shim it to fit.
Try here..... http://www.ebay.co.uk/itm/111083467...eName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 2.75mm will work just fine Here fitted to a SVEA 8) & a Radius 42 Stu
Looks like you are in the US - eBay - French Winding Key Fettling Forum - Svea Regulating Keys, Pot Handles and Windscreens
Thank you loco7stove! After I figured out I wasn't going to find a original key, my next question was exactly were you led me. You must be a mind reader. Thanks again, I'm, ordering a 2.75mm key today. Great links BTW!!