You can find comprehensive collections and individual works at several reputable digital libraries:

Books by the (Оптинские старцы) are widely available for download in various digital formats including EPUB, FB2, PDF, and TXT . These works provide spiritual guidance on humility, prayer, and Christian living, drawing from the legacy of the 14 canonized elders of the Optina Monastery. Where to Download

Учение Оптинских старцев - Виталий Кандалинцев