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They must have recently updated their website. This is the new link:
Slate Honing Stones for sale by Inigo Jones

I doubt a coarse surface will make the DT act coarser for honing. It will be somewhat different I'm sure but will it be helpful? Let us know when you tried it.

With the slurry stone you'll get you...

When you order three or more stones at once you can ask for a discount. I once bought three and only paid shipping for two. So a group order should lower the expensive shipping costs to the US.