Yeah, the chalice is the hardest object to find, because it was thrown in as an optional extra and isn't really signposted. I should probably update with a clue or two.
But as a hint, the chalice is in the possession of Lord Pixby-Bitsington, an egotistical renegade cat lord, and founder of Meowich. He's currently hiding from the Dread Sorceress, but where would he hide?