There is a path of sorcery in Frontier secrets for Werewolf the Wild West. It is called Saturnalia and it allows you to summon and command both spirits and ghosts. Also in Dreamspeakers revised there is a whole shamanistic sorceror setup, it has four different paths having to do with the spirit world, while they focus on spirits of the middle umbra it should be fairly easy to convert them to necromantic powers.