The best cobs, I've found, can be gotten at the pet store. We have a PetSmart and a PetCo close that have packages of very small cobs for pet feed (Hamsters and such). I use regular inkjet ink (I suppose that any ink would do) to soak them in, then dry and turn, using CA most of the way through the process. Finely I finish the pen with a buffed out coat of CA.
I carry a throw-around pen, that I made this way about 3 years ago, in my pants pocket every day and it still looks almost like new.... except for the pen plating.
Al