Radio Shack does sell the pens, but they are special order only.. no big deal...go to your nearest Radio Shack store, and in the catalog, (don't have one with me now), you will find a circuit board kit that you can make a custom circuit on. Part of that kit is a resist pen used to repair circuit boards... you don' have to buy the whole kit though, as the pen is also sold seperatly for $ 2.98....
and you can't find it on line either...just in their catalog..
They will order it for you and have it shipped to your door, takes about 5 days to get it....
ps: there is also a a different resist pen in their catalog for $ 15, you don't need that one...the $ 2.98 one works fine