Long time ago i bought this slip stones they were 4/8k and performs excellent.i tried to find the link unfortunately couldn't.This is the exact similar stone but it is 1k just have idea.check woodcraft maybe they have it.it is alot cheaper and does the job.i clued them together and use as a norton 4/8k combination stone.it fits inside your hand very light .does good job.
Buy Slipstone, Waterstone, 1000 Grit

hope this helps