DLC Weapons for Dark Souls 3 are categorized in this page. The DLC is sold separately from the game, in two installments called "Ashes of Ariandel" and (unknown). You can see the full list of all weapons in the game in the weapons page.
Ashes of Ariandel DLC Weapons in Dark Souls 3 are listed on this page. You must purchase the DLC to be able to obtain these weapons normally, but they can be traded.
Ashes of Ariandel DLC Weapons List