Where to find Western-Style Stone?

I'm in the process of trying to make a haunted island and a friend gave me the Western-style Stone. It's exactly what I'm looking for, but when I tried to purchase more of them using the Nook Shopping option, it's 'Not for Sale'.

Does anyone know where these come from or why they're not for sale? Is it because it's a locked DIY? Or is it a specific item you only get one of? Or obtained through special means like Gulliver's items, etc? I've looked online, but there's no information about them that I've been able to find.

i learned this recipe from a bottle on the beach, it requires 30 stone to make each one

Allytria said:

Hey there!
I unlocked this DIY recipe from visiting a neighbor who was working on the workbench! I hope that helps! c:

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Thank you very much! I appreciate the help!
Here's hoping I get lucky and can run into a neighbor working on one!