I'm going to assume you're just talking about the unique search token in the first encounter of The Cardinal's Plight; if that's not right, let me know what quest you are looking at.
The Relic is just the unique search token. There's no card associated with it, and the only thing the heroes get from it is opening the locked door in the encounter.
REALLY? Like the OP, we searched like mad for a "Relic of Dawn" card, and ultimately just decided that the Staff of Light referenced in the boxed text must be it.