For completing the Gunslinger Side Quest in Dying Light you will need 9mm Pistol. You can look out for this weapon rather early in the game.
If you are expecting it in the form of loot from human enemies then you will be rather disappointed as they only carry rifles and melee weapons. Go through the following guide to find Dying Light 9mm Pistol for Completing Gunslinger Side Quest.
You can get the pistol in two different ways, one is to get it from the cottage in the bottom right corner of the slums. This weapon will frequently spawn in this area. Another way is to lockpick police vans. Look for them on highways and bring some lockpicks.
The 9mm Pistol plays an important role in completing Gunslinger Side Quest from the upper tower in the slums. By completing this quest you will have access to a pawn shop that contains two text collectibles. Which is important for collectible hunting.
If you are still not sure, watch the following video on how to get the Dying Light 9mm Pistol for Completing Gunslinger Side Quest:
Dying Light is a zombie apocalypse-themed game set in an open world. Players traverse an expansive urban environment overrun by a vicious pandemic, scavenging the world for supplies and crafting weapons to defend against the growing infected population with a heavy focus on freerunning mechanics.
Players assume the role of Kyle Crane (Roger Craig Smith), an undercover operative sent to infiltrate the quarantine zone in the fictional city of Harran, based off ancient Turkey, as his mission is to find Kadir "Rais" Sulaiman (Michael Hollick), a rogue agent who has a file that could destroy the reputation of the agency. This game is now available on PC, PS4 and Xbox One.