There may be better answers, but I have extracted images from the Art Book that's included as an extra with Thronebreaker on GOG. That has some double page images that you can stitch together into one (including the crones), so it wasn't zero hassle, but that is an option. Another (even more hassle) option would be to get and learn how to use a unity assets unpacker and find the loading screen images. Or just get the card images (either by extracting or looking on gwent.one or reddit) and stick them together yourself, hoping they are seamless.
Oh, and have a look on the website Artstation, a lot of the Gwent artists put their stuff up there in original form, so you may have luck with that.