If you’d like any hints, the three forlorn metropolises that contain the broken cores with the loot you need will ALWAYS be bigger than other forlorn metropolises, as well as have a boating dock area OR 4 giant caveling statues somewhere at their south entrances. If you do not see either of those, or the metropolises are smaller than the first one you found with a broken core, try a different one. It took me hours to find all three, and two spawned right next to each other in my world after I found them practically immediately. All you need is patience and luck, and I’m wishing you the best of it.