All I need is an item that'll be used by the mon or a two-turn move quickened by Power Herb.
Unburden users who can learn Fake Out often use Normal Gem as a fairly risk-free way to consume their item. You can buy Normal Gem from Delibird Presents in Cascarrafa; ever since XY it's been the only gem that they actually bother to include in the game.
As of Scarlet and Violet, the only move Sneasler has that can be boosted by power herb is Dig, which isn't really viable unless you want to catch a random electric type off guard. Your best options are one of the Seeds that activate when in respective terrains, a Focus Sash, or an item that has a powerful effect when used by Fling, but that's a one-off that could easily be wasted if used incorrectly. If I were you, I'd go with the Sash or a Seed