I've got twenty-six different shaders, but the only ones I've gotten from a Tower NPC have all been from the Cryptarch. Edit: Seems that other people here have gotten stuff like Bittersteel from getting faction NPCs to level 10 or higher. If that's true, then that's really disappointing since factions like Dead Orbit and Future War Cult have some pretty lackluster weapon and armor rewards. Having to grind out rep just to get a shader is just... well, it's another thing for me to add to my long list of existing complaints (not that Bungie seems to care).