Clementoni 35132 ColorBoom Collection-Stairs-500 Pieces-Adult, Color, Puzzle Gradient, Made in Italy, Multi-Coloured : Amazon.co.uk: Toys & Games
1000 Piece Gradient Puzzle – Southbank Centre Shop
Another gradient puzzle from Areaware, 500 pieces. There are some false matches with the shape and fit, and the gradient only spans horizontally and over a small color range, but I could