Archives older than those present here have been removed from the Gildas webpage,
but you can still download them anonymously through GIT, e.g.

git clone -b r22-dec git@git.iram.fr:gildas/gildas.git gildas-src-dec22

Note the monthly branches naming convention: "r" for release, "22" for year
2022, "dec" for December. The target directory name is your free choice.

However, we strongly warn you that:
1) the newest versions of Gildas have bugs fixes and new features that you will
   miss if using such an old version (see e.g. the NEWS section on Gildas
   webpage),
2) the Gildas Data formats are evolving (keep an eye on the NEWS). Old versions
   of Gildas won't be able to read them,
3) there is no warranty that you will find a suitable Fortran compiler.