Delta Green: Impossible Landscapes is available in PDF and ships in hardback in June 2021. Its PDF edition comes free with every print order of the massive, full-color hardback (though sometimes it takes a day or two to reach your inbox). And you can order the PDF by itself along with a comprehensive collection of handout images at DriveThruRPG.
Written and illustrated by Dennis Detwiller, Impossible Landscapes sees Agents exploring the depths of meaning and madness in the strange, surreal phenomenon known as the King in Yellow: a play, a virus of the mind, a king whom emperors have served, a crystallization of understanding of the unfathomable nature of reality. Once your Agents have seen the Yellow Sign, they will never be the same.