I'm not 100% sure but I don't think that is black hammertone paint. All the Nye keys I've had & seen have a sort of black 'wrinkle' paint finish. Well, not exactly a true wrinkle but a rough 'textured' finish anyway. Almost like it is a 'flocked' paint.
However, in either case (depending on the location and size of the area) it is difficult to touch up either hammertone or wrinkle paint and achieve a match. The reason being is that the ultimate look of the finish is a result of a number of factors. For example, the 'wrinkle factor' is affected by how fast it dries (temperature) and/or how thick the paint is applied. A Hammertone finish is a result of a sort of 'chemical reaction' and the results are also affected by temp, etc. and *especially* color matching.
Unless it is a very small area you would probably have better results by repainting the whole base instead of trying to touch up a spot.
But to answer your question, a quick search on google shows both black hammertone & wrinkle paint can be found at Eastwood auto parts:http://www.appealingauto.com/wrinkle-paint-black-aerosol-12-oz.htmlhttp://www.eastwoodco.com/email/default.asp?T1=10014Z&SRCCODE=1CJBAN8