Grand Master Samael:
The Archon of Halisha has the next Stone of Commune.
You can find the Archon inside the Four Sepulchers in the Imperial Tomb. You mustn't enter that dreadful place alone!
If you're unable to form a party for some reason, massacre the Archon's minions in the Shrine of the Loyal. Kill enough of them, say around 700, and he will appear.
His minions are called Grave Scarabs, Scavenger Scarabs, Grave Ants, Scavenger Ants, Shrine Knights and Shrine Guards.
The Tablet of Vision that you seek can be found on the road to Goddard from the Wall of Argos.