The Spiritist is located near the Sunken Isles. Follow the path down from the Promethean Keep and to the beach and you will see an island across the way. Located on this island is a shrine, and just past the shrine is the Spiritist. Here all the books of the Animist (regarding magic), plus Spiritism and Ahk Manifestation are sold for 250s each.

Anyone who wishes to add pictures or a more detailed explanation is more than welcome to do so.

Thanks are given to Rathius, of the Aegis Imperium, for sharing this information with us.