where to find "shell"?

[Belial]

Cool story, bro. Did you bother to read it? Because it specifically mentions that protect and shell will overwrite each other but there is nary a shell-giving action in there.

To the OP, this item will give you shell.

See:

Conjurers also get a trait that adds magic defense into Protect, but the Shell spell itself is gone.

Which can be located... *drum roll*... in the patch notes.