https://www.pcgamer.com/fortnite-adds-playground-mode-and-dual-pistols/

Fortnite's latest v4.5 patch adds Playground Mode, a new slant on the Final Fight limited-time event mode, and dual pistols. Prance around the battlefield like Neo from the Matrix, Travis Bickle from Taxi Driver, Doomguy from Doom, or some other more contemporary double gun wielder. 

From back to front, Fortnite Battle Royale's Dual Pistols come in Epic and Legendary variants and deal 41-43 base damage with Medium Ammo. They don't use first shot accuracy, this update post explains, and can be found in chests, supply drops and as floor loot. They look like this: