Trader generaly spawns 8 KM away from starting point of map. You can find him easy if you just go in circle araund that area and icon should show on map.

(be sure you carry portal mats in your boat -- some copper also to set up a new base)

In meantime you can also just map the map this way. (and look for swamp dungeons from sea and also mark those for future iron)

Elder spawn location stone could be found near stone towers or inside dungeons. Its not 100% as its rng.
Morder location is more pain to find tho.

Oh and watch out for water snakes