At Woodcraft -BUT- don't get hung up on the Nagura you can use just about anything to raise a cutting slurry, even those small cheap DMT credit card sized hones... I have used an Arkansas stone a Coticule even a few real Japanese Nagura stones :) the Norton prep stone is rather pricey I think the other ones are much cheaper and work the same normally you can find them for $8 by Googling "Artificial Nagura"