A Whistle of the Hound Master seems to be made of an obsidian like material and is carved in the shape of a howling wolf.

The whistle has 1d4 + 3 wolves.

As a bonus action on your turn, you can call a wolf from the whistle. The wolf instantly forms from a cloud of red smoke that pours from the whistle as you blow through it, fully forming in an unoccupied space next to you, and acts on your initiative count. The wolf can tell friendly creatures from hostile ones and attacks the latter. The wolf disappears in a harmless puff of smoke after 1 hour, or when you dismiss it (no action required), and returns to the whistle. If it drops to 0 hit points, the wolf can’t return to the whistle. When the whistle doesn't have any wolves to summon, the whistle becomes a nonmagical item.

Notes: Summoning