On that page you linked to, look at the Copyright Notice at the bottom - that tells you what book it was originally published in.
Since it was originally in an adventure path, I wouldn't call that an official item - I'd bet it's just something they created to throw onto an NPC. Remember that d20pfsrd does their best to find all the items in everything Paizo has published, but it's up to your GM whether to allow that item or not, since it's not from a rule book.
However, in Hero Lab, I just checked, and if the "Curse of the Crimson Throne" adventure path is turned on (that path was issues 7-12), Celestial Plate Armor is an option to purchase in the magic, custom & masterwork armor table.