Perhaps the most important resource is the audio recording of this speech made by Cardinal Cardijn at the Domus Mariae Centre in Rome on 29 November 1965, days before the end of the Second Vatican Council and now online at the Catholic University of Leuven Centre for the Study of the Second Vatican Council:
L'Apostolat des ouvriers
Wij Herdenken Kardinaal Cardijn
This is a recording of Cardijn talks. Not available for listening online.