Any cutlery store should have them, any sporting goods store, and Wallyworld type store in the sporting goods section, any hardware store (they usually have a portable glass fronted case with knife and some stones, many times located near the checkout). I have many diffrerent type so sharpening tools, for what you want I would suggest a diamond type of "stone," either a small flat one, or my latest carry tool, one of the long skinny types, flat on one side, the rest round, which stores in a case about the size of a ball point pen (I tried to find a pic to post and couldn't). Diamond is nice because you don't need oil, water, anything, to use it...