The ones such as the 'dogbone' stones or gatco tri-sharps, are simply 3" sections of triangle stone. They usually sell for about $10 each up here.
The B&M knife shop up here buys extra whites and cuts them using a ceramic cutting blade(about $25-30), and chops off 3" sections and then sells for $4(vs 10, save $6).
Thats why I said to buy a "replacment stone" for the 204, and chop it. I bought one of the small chunks from the store, and then bought the 303MF for PE, and finally bought a 204MF. I'm on my 2nd 303MF(lost the first one when I was walking to the PO in Aug) and still carry a small chunk of spyderco white triangle in my car.