I've had a little try for silkstone (on the net) with no hits (if thats the correct term).
I trawl the flea markets and antique shops, but often the hones I have seen don't have boxes or any identifying marks.
What I should do, is buy the hone (if it's very cheap) if it feels fine enough for razors, post pictures of it/them here and see if anyone recognises the type of stone.
I found you eschers and silkstone pictures on flicker, any chance of them finding their way to SRP?
How big are your Silkstones? Can you describe them?
cheers Marcus