I actually found that cabin quite some time before I got the quest, but it wouldn't let me in at the time. If you leave Crossroad Keep and head to the east, once you get around the rocks, go almost directly northeast and you should find it. It's only a very short distance inside the woods.
EDIT: Updated the list with most of the missing information:
Inshula Sar Mashewe. Human Ranger (in the Samargol market)
Quarrel, Half Drow Warlock (in West Harbour)
Soraevora Aeravand, Sun Elf Favored Soul (in Crossroad Keep)
Septimund. Doomguide of Kelemvor (in Port Llast)
Umoja, Human Druid (in the Samargol market)