You can easily make your own with a canvas, a paint brush, masking tape, and three colors + white acrylic paint. Just tape up your canvas every which way, paint a gradient of each color in the taped segments and remove the tape
"Vertical Landscape" by Eiko Ojala. It looks like a paper landscape but the artist actually works digitally and hand-draws all the elements to look like they're cut out of people. (Hint: the shadows help!