All three Darkspore Portal is Randomly generated. You should come across the portal from Paradise Isle if you go West towards Artellus Town. If it's not there then it could be north of Dhalium Town or East of the Infested Cave.
I complete the king's request, find one near Dhalium Town, and find another one near Infested Cave, but I can't find the last one, very strange.
As I mentioned it's RNG, you may not find the last one near Paradise Isle, it could appear back in Dhalium Town or Infested Cave.
