Let me clear this up for everybody. I've completed the Dawnguard side of the DLC and I now own an Enhanced Dwarven Crossbow which fires Dwarven bolts. I got this by doing the Ancient Technology quests for Sorine Jurard after you get your first steel crossbow. The first quest is to find the schematic for an enhanced one, then 3 more quests to get fire, ice, and shock exploding bolts. After that, you do a quest to get the Dwarven crossbow schematics and finally, a last quest to get an Enhanced Dwarven Crossbow. You can craft Dwarven bolts or recover them from Dwemer machines. The Dwarven crossbow with Dwarven bolts is one of the most powerful ranged weapons, excluding the Dragonbone bow. These are the only 2 types of crossbows.