An Implant Without a Source

Implant: Sleek Stroke exists in the game's item data, but no shop, loot table, or reward currently hands it out — and the Pal Surgery Table never asks for it. It's an unused leftover: you can't get it, and you don't need it.

How to Get Sleek Stroke Anyway

The passive this implant would unlock, Sleek Stroke (Swim Speed +30%), is one of the default options at every Pal Surgery Table — no implant needed, just 10,000 gold per surgery. The bigger swim tiers do need items: Ace Swimmer comes from Implant: Ace Swimmer and King of the Waves from a disposable implant. See the implants guide for how surgery works and which implants are actually obtainable.