There are several blueprints around Dunwall you will come across that upgrades gadgets. If you get the blueprint, you are abled to buy the gadget at Piero.
Bonded Galvani Weave: Improved armour
You'll find this at the back of the Overseer's mansion, in the workshop. It is in the Safe.
Sokolov's Formula: Health Elixirs
Once you save Griff - you can buy it from him.
Lens Magnification: Improved lens magnification
Once you save Griff - you can buy it from him.
Lens Magnification 2: Improved lens magnification
Buy from Griff at his pawnshop.
Incandescent Paste: Fire bolts
At the distillery, behind the door that is controled by a valve (the door that shuts after you open it with the valve).
Folded Galvani Resin: Upgraded Boot Stealth
At the beginning of the mission, at the first bridge area go to the left side of the river and go into the warehouse.
Sokolov's Formula: Health Elixirs
Inside Sokolov's mansion, go to the workshop and library to green house.
Spiked Grenade Housing: Sticky Grenade
Near the gate of Boyle's Mansion is the guard room/post, it can be found there.
Small Scale Combustion Refinement: Explosive Bullets
In the General's business office in the Dunwall Tower. It is located in one of the four central offices.
Incandescent Paste: Fire bolts
In the lower left cellar, by the tunnel's exit.
Spiked Grenade Housing: Sticky Grenade
Inside the building full of armed thugs, look in the damaged hallway.
Small Scale Combustion Refinement: Explosive Bullets
Central Rail Station: inside a crashed train car.
Folded Galvani Resin: Upgraded Boot Stealth
Inside Daud's office. In the unlocked chest.
Bonded Galvani Weave: Improved Armour
Inside Duad's office. In the locked chest.