It can be obtained in a chest in the Misty Cavern.
Zul's Toy one of the weapons shown in the early official screenshots released by From Software for Forever Kingdom, along with the Soltan Sword, the Seculian Sword, the Seculian Loops, and the Frying Pan.
Zul's Toy, the Frying Pan and the Umbrella among the earliest weapons to be shown through early test screenshots.
Zul's Toy in use
If you can get it this early in the game, that is.