You can find the english (Text) files for download in GitHub where the program Code is.
Conversion to mp3 files may need some effort using a tts site like https://ttsmp3.com/.
As far as I know, there are no ready-to-use mp3 files available for latest program versions.
If No mp3 Download ist available from the Site you can use audacity for recording the Output of your soundcard as described Here: Mitschnitt der Soundkarten-Ausgabe
Hope this helps and your time and skills allow to make it.