Finding them is simplified if you embark on top of them by making a monster island. Though, untamed roc aviary seems even more of a tempting weapon to me.
Here are some ideas, off the top of my head, for long-term fort(s)/projects:
◙ Generational fortress/breeding program. Selection of the fittest! If combined with below, then vamping of the fittest!
◙ Metropolis populated entirely by <x> race, where x is not dwarves. Got Cacame? He needs his subjects.
◙ Walling in targets with long embarks and strong military population. Perhaps embarking on a thin strip of land connecting the goblins conquering everything to the rest of the world, so that they will have to pass through your embark tile - then killing that goblin civ - maybe after they killed the original dwarves?
◙ Killing every kea in the world. Expansion: Killing everything and bringing age of death/emptiness.
◙ Instead of killing the elves by showing your wood and then bitchslapping them, killing elves by sending infected saboteurs back to their forest retreats after they visited your library/tavern.
◙ Embarking under an ocean, in hell, then breaching through the adamantine spires to build a spire reaching to the sky. Dfhack would be necessary to get migrants, though.