You should be able to easily get this organically by running the Daily Dungeon from Rhix in the Protector's Enclave. The Daily Dungeon becomes available at level 14 and is a good way to get 3,000 Rough Astral Diamonds. You can run it every 20 hours. If you're playing the game normally, this won't be a problem.
NOTE: as pointed out in comments, this is glitched as of May 5th, 2015. Hopefully update will fix. The Epic version of this, Dungreon Master, is also glitched. Watch the "RECENT WINNERS" box on the right -- until you see it move from "05 May", it is still bugged. If they ever fix it, it will coincide with an update, so when you get an update come back here a day later and check if RECENT WINNERS has moved, if so you'll know it's fixed.