To buy the event hammer, you need to use the in-game store for the event monkey. Click the monkey on the starting island, then click "play now" to enter the stage. On the lower right, there is a series of buttons - you want to click the blue one with the $ on it to access the general store. In the store, click the "Hammers" tab and you'll find the event hammer available to purchase.

Thank you Tabitha for helping. Best of luck to you both.