I can tell you where the first one is. The first one is by one of the areas that those spawning platforms are. It's a big panorama of the dreadnought. I saw a platform within range to the side of the one we were on and a platform appeared. I hoped over and killed some thrall and to the right there was a calcified fragment. Then the two thee ones where in the crawling holes you find in some of the rooms on the dread naught. Have found 4 so far including these 3. All I know is we finished that mission with 3 and Eris gave us a quest to find 5 more. So now I need 4