Silver Shovel: Donate enough specimens to the museum on Main Street to unlock the second-floor expansion as a public work project. Complete the project, then visit the museum's second-floor shop daily to see if the silver shovel might be for sale. the silver shovel gives you a 10 percent greater chance of finding Bells when you smack rocks with a shovel.
Golden Shovel: Purchase 50 bags of fertilizer from Leif at the gardening store, and he will reward you with a golden shovel. This super shovel lets you grow trees that sprout bags of bells simply by planting bells in the ground.