Here's a tip for getting a few of the gates the easy way if you have it available to you:

Sorel Haven - In one of the Archer quests (I think L36) you will enter an instance near Sorel Haven. If you zone out of the instance here you'll end up near Sorel Haven and can snag the gate.

Lichenweed - Upon first using the echo in the Gridanian storyline you'll enter an instance up near this location. Zone out of the instance and you can snag the gate with ease.