Expedition characters locked

so im level 79 and only have Gwenyn unlocked out of the 4 expedition characters, i assume i need to complete the quest "Explosive Archeology" (talk to Gwen after and encouter) in order to progress to unlock the other 3. HOWEVER, I out level the zones in which this quest would be completed (Act 6), as in none of the late game content is spawning. So im wonder if there is another way to unlock them?