The slavers who attacked you in Blightmarsh came from Anselm's Landing, so if the tribespeople they captured were taken back here, they might still be around.
The slave market is a vast warehouse at the end of a wide street. A colossal pair of wooden doors, bound with bronze, takes up most of the wall of the building that faces you. Into one of the doors is set a smaller door, the size that a person might fit through. You walk up to the door and knock on it. A moment later, it opens a crack and a man's voice comes from inside.
"What is it?" he says. "What do you want?"
"I'm looking for some slaves," you say. "Only they're not slaves—they're members of the Tribe of the Red Bear who are under my protection. I have come to claim them."
The man hesitates. "I see a lot of slaves coming through here," he says. "It's hard to remember any specifics."