To unlock this achievement you will need to find and collect all of the melee weapons within the game. Unlike with the firearms, you do not need to complete the mission with them still in your inventory, you just need to pick them up, then you are free to drop them. You will begin every mission with the fiber wire and the syringe, so I won't list them.
The Fire Poker can be found during 2 different missions, 'The Bjarkhov Bomb' near the fireplace in the station where Fabian Fuchs is dining and during 'Beldingford Manor', again near a fireplace, inside the manor.
Pool Cue's can be found during 3 different missions, each time on or near a pool table. These 3 missions are; 'Beldingford Manor' on the second floor, 'Rendezvous in Rotterdam', in the bar and 'Deadly Cargo', on the second floor of the bar.
The Shovel can only be found during 1 mission, which is 'Beldingford Manor' and it is in the center of the hedge-maze.
The Stun Gun can only be found during 1 mission, which is 'Asylum Aftermath', being carried by the asylum's staff.
The Kitchen Knife can be found during 7 different missions. During 'The Meat King's Party' and 'Rendezvous in Rotterdam', you can find them in lots of various places. During 'The Seafood Massacre' and 'The Lee Hong Assassination', a chef will be wielding the knife. During 'Asylum Aftermath', you will find it being used by a patient who is butchering a clone on the second floor. During 'Deadly Cargo', you can find 1 in the galley of the ship, or in the kitchen of the police station. The final place where you will find a kitchen knife is during the mission 'Traditions of the Trade', where it will be stuck in a wall at the murder scene in room 109.
The Meat Cleaver can be found during 2 different missions, which are; 'The Meat King's Party', in the kitchen and being carried by Malcolm Sturrock, as well as on the mission 'The Lee Hong Assassination', being carried by a chef in the kitchen, and 1 in the basement.
You will begin the mission, 'The Meat King's Party', with this weapon in your possession.
The Bolt Gun can only be found during 1 mission, 'The Meat King's Party', where it will be in the main butchery area.
The Chinese Sword can only be found during 1 mission, 'The Lee Hong Assassination', where it is being carried by Lee Hong.
You can find a pillow during the mission 'Beldingford Manor'. It will be in a second floor bedroom, where you will find 1 of your targets, 'Winston Beldingford'.