This is what the EdgeCraft corporation (makers of your sharpener) have to say about replacement stones.
Used in a household setting, the abrasives will last for many, many years without need for repair or replacement. If the abrasives need replacement, you may send the sharpener back to EdgeCraft and, for a nominal fee, EdgeCraft will replace the abrasives, clean and lubricate the sharpener and ship it back in almost new condition. The abrasives, however, should last a very long time with normal household use.
Here is their contact details
Hopefully this is of some help.