I know that MoviePosterDB (www.movieposterdb.com
) featured a lot of the key art from the Indiana Jones films, books and more but the website is currently offline. That said, the two guys that ran it parted ways (one to start CineMaterial: https://www.cinematerial.com
) and both websites' content is nowhere near as extensive as it used to be on their original site. I get the impression the movie studios 'politely asked' them to remove their copyrighted content.
You need to hunt down a website that offers 'key art'. I quick look by myself just found a few items like the one below but maybe a more thorough search could turn up what you're looking for