On Fjordur their eggs spawn in the back of the wyvern trench you can enter from a cave located near the wyvern trench on the side closest to the obelisk. I recommend a maewing with decent HP and Melee to enter near the start of the magmasaur cave. The inside of the magmasaur cave is very hot so i recommend ascendant ghillie (i am not even hot when wearing ghillie). Inside the cave is element shards (redish rocks near the back inside a nest and near the middle on a small side piece of land), crystal, metal and BLACK PEARLS!!! Nests spawn in the middle with the lava lake. I recommend to go inside the cave a strong tame (i go overboard and use a strong carch with a very good saddle doing 4k damage on max rage.