There's a quest from the remain of....something (the competitive misison, you know?) where you have to go back to Sulferous Waste to do it. It's about Abaddon's Temple something. There're tons of Graven Monoliths at the place. You can go there and kill the mobs over and over until you get enough shards (The temple is like a small room so it's not that hard to kill them all at once).
But from my experience, just do the quest at the temple normally and you should get enough to finish Sticks and Stones. Trust me, you have to kill tons of them in this quest anyway.
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