I use Math Type, which is the pay version of Equation Editor. The N and C are included in Math Type, but I can't check Equation Editor as Math Type installs itself over Equation Editor. I know one of the selling features for upgrading is that Math Type has more symbols.
Try this. I've made a document that contains N and C made from Math Type. Maybe you can open it and copy and paste them into your document. http://orbitsimulator.com/misc/nc.rtf