Correct me if I'm wrong, but isn't that already in the game?
There is not, however, there is another similar weapon in game which shows why this suggestion will not make it through:
In game right now, there is a 'knockback sword'. This is a wooden sword with knockback II with a durability for about 3/4 hits. The weapon right now is super overpowered: You can kill a full diamond by hitting them once on the edge, since they will fly off. Right now, the item is pretty decent balanced in my opinion, as the durability allows you to kill between 0 and 2 users with it before it breaks. In overpowered, the weapon has more (in my opinion too much) durability, so that's a whole other story.
Adding a knockback stick would be very unbalanced, as it has unlimited durability. The knockback sword works perfectly fine in the lucky islands meta, and that's why I think this item should not be added.