There is some parts of a panoply, quite famously from Italy from the 15th Century. I have seen photos of it. But it was apparently for tournament with 'whalebone' weapons. Kind of like the 15th Century equivalent of LARP ;)
The only authentic purely leather armor I've seen so far is from Asia, mainly Central Asia but also Japan and Korea. They have armor made of out of Elephant, Rhino or Crocodile hide in South Asia, and in Europe there is a lot of armor made of combinations of leather with textile and / or iron.
G