I'm not so sure about leather. Most third party products tend to be polyurethane or other artificial material based. There usually are a few leather cases but I don't recall there ever being third party leather smart covers for previous iPads. I have one made by Grove in the US but that came with a wooden back case which I never used. I only used the Smart Cover although the bit connecting the magnets to the actual cover was a bit lose.
I just wish Apple hadn't made the decision to stop offering the leather smart covers. I might have to resort to getting one of the official Apple poly ones for now. I just hope one of the third party companies offer a TPU back case at launch.