This is a plus-size custom-sized dress from Lady Sloth. The dress also has back shirring to fit a variety of measurements. The dress has since been discontinued on the Lady Sloth website, so if you love artwork prints this is a good chance to buy an older piece. The dress is in good condition just a bit wrinkly but that can easily be fixed. 

Measurements:
Bust: 41-46" max
Waist: 37-42" max
Length of skirt portion: 22.5"
Sleeve: 17"