I have a Dembart Hand tool with 2 or 3 cutters. Call Brownells and ask one of the techs. Can't remember what cutter I used. It is painstaking.
When the stocks (grips) are worn realize that it is like peaks and valleys. When worn the peaks are gone (wood loss) so even cutting the valleys the peaks on the worn spot will not be the same
You also need to strip the old finish and apply a new finish. I have refinished several sets of grips, they are better but still not like new. To have someone do it is (to me) not worth the price for two pieces of wood.