Lengua Española: Comprensión is LLPSI: Familia Romana of Hans Ørberg. The equivalent courses for some of the other languages are L'italiano secondo il metodo natura, English By The Nature Method, Le Français Par La Méthode Nature, Deutch nach der naturmethode and Dansk efter naturmethoden.
You can download the pdf file which contains the entire book and the key from archive.org
You can order an original physical copy of the book from Amazon here.
For the audio recordings see the index here.