Obtaining a matching whetstone - same abrasiveness etc

I have a small whetstone that I like, and I wish to get another of the same ilk. I like them small – I like to hold the whetstone in my hand and move it against a stationary knife instead of moving a knife against a large motionless whetstone. But that does mean they wear down more quickly (since there’s less of them to begin with).

I live on Long Island. Where might I find a store with competent personnel who can match the general abrasiveness and coarseness etc of an existing whetstone? Is that something I should assume any store that sells knives and sharpening stones would do, or do I need to seek out some kind of specialist store (or a professional knife grinder or whatever)?

Lee Valley is a good place to start and they deliver to your door. Very handy if you know what grits you run already.
https://www.leevalley.com/en-ca/search#q=whetstone&t=product-search-tab&sort=relevancy&layout=card&numberOfResults=25

Probably not the best deals, but both Sur La Table & Williams-Sonoma carry them. There should be one or both stores in your area.

This is exactly what I don’t know. I want to bring it in to someone and have them say “Aah, yes, this is an 800-coarseness whetstone, and I can show you the ones we have that have approximately that abrasiveness”.

I don’t know how to find out.

If you have a store near you they are pretty helpful.

I think the knife grinder idea is probably a good one. Anyone who’s been doing this professionally for a while can probably identify the coarseness by sight.