I have seen them in shops. I wouldn't think you would need a special pattern, I would purchase a pillow in a size & color you like (thrift stores might be a good source). since you are going to add a quilt block, a pillow that will accommodate a 12 inch square would be a good size. Get 4 decorative buttons & sew them in the corners, then just make a mini quilt/ quilt block, bind and add button holes.