I was doing a challenge run where I only use the NPC slaves, I couldn't buy or catch any other ones. It was fun but I've hit a roadblock and that's when you have to give a elf and a dark elf to that lady in the lone hut.
I already had to make my starting slave a Taurus for the laboratory quest, and there are no NPC dark elves. So my last chance is to somehow find whichever game version had Ivran as a dark elf and use that.