I looked everywhere for Wantz, couldn't find him. I even saw a picture of where he was, and i still couldn't find him. Maybe I didn't progress far enough yet. I have the airship, but I haven't fought sin on the top there, maybe he'll be there after that.

You're right about monster at the omega ruins dropping tetra stuff. I got one armor with 4 slots, but one of them were already taken by a useless auto-ability, i don't remember which it was, but i'll probably find an empty one some day