I'll attach the core just in case, because finding older versions of Retro Arch seems to be an annoying task.
Older versions can be found if you go to: https://buildbot.libretro.com/stable/
After that, pick a version, then the platform, and download the zip file.
But if you mean older ones like 1.8.X, let me know as I know of a certain Spanish site that has couple older versions.