Accessory Life Stones are for Augmenting Jewelry, and you get them from Blacksmith in any town by exchanging 5 standard Life Stones(no grade) of the same level.
Maestro Ishuma is at Gludio Airship Dock, Vesper is no longer S-84, it's S-80... but for some reason Blacksmiths exchange window for Accessory Life Stone - Level 84 still has the same description as your link(Accessory Life Stone - Level 80 should work for Vesper Jewelry too)
"Enhance Stone that raises up the power of a Vesper item. Can be exchanged with a Vesper Noble item through Maestro Ishuma."
use it where?
The description in-game is a mistranslation. It's a regular Accessory Life Stone that you can receive through any Blacksmith NPC. The Accessory Life Stone can be used to augment earrings, rings, and necklaces.