Where can I get/buy these audiobooks?
I purchased them through Audible. They don't have everything I would like, but there's a decent selection.
The Sinner's Guide
The Spiritual Combat
The Spiritual Exercises (read by Kevin O'Brien)
The Mystical City of God
The Spiritual Doctrine of Fr. Louis Lallemant
Humility of Heart
There are many more available, but any one of the above is to be considered a treasure.