Paint your own, JHB. It’s really not as difficult as it sounds. Barry Norman’s book on scenery tells you how. It’s based on ever thinner washes of green. Here’s a crude one I made this week. The idea of a backscene, I think, is to provide just enough depth to fool the eye into focusing on what’s in the foreground. Look at a lot of coloured photos of Irish railways and what you see in the background is a vague sweep of green and brown. Note that you will have to specifically focus away from the railway content to do that! As long as there’s a suggestion of. appropriate background, your brain will paint in the rest. It’s a basic camouflage technique - just providing enough visual clues for you to see what you are ‘meant’ to see.
Photo backscenes are fine but sometimes too sharp and actually distract the eye towards them…well that’s my rationale anyway! The lowest layers of this one will have 3D scenery in front, but will hopefully give the idea of that classic Connaught high ground behind.