I tapped my Magikarp too much and the Everstone broke. How can I get another one?
EDIT: I have evolved one Magikarp so far, and I haven't got an Everstone.
EDIT EDIT: it turns out you do get a new Everstone after a Magikarp evolves.
You do get a new Everstone after one breaks and a Magikarp evolves.
Source: Check under EDIT EDIT.