You should buy a copy: GOG or Steam
For packaged versions of these mods see Steam or Nexus Mods.
Place mod folder(s) in %AppData%\Surviving Mars\Mods (Create "Mods" folder if it doesn't exist)
https://pcgamingwiki.com/wiki/Surviving_Mars#Save_game_data_location (other OS locations)
Enable with in-game mod manager