You just need to keep persevering with the Dark Caves adventure. I had a quick skim through the discussion thread and most players had received it by about adventure 9 or 10 (if not before). It's 150 gems to skip and personally I wouldn't gem skip, but it's up to you of course. Without the pictures, I can't see if you need it for anything else or if it's part of future crafts. Maybe someone who is doing this storyline at present can post about it. I wish you luck!