There is no single "pirate bay" for his works. The best aggregator is Archive.org for old scans, followed by Google Books for clean, searchable PDFs.
Another official platform featuring SKY Kalanjiyam and educational materials. E-Books Platform Vethathiri Maharishi Books Pdf Tamil
Vethathiri specifically designed his books so that the written word acts as the Guru. He stated that reading his books with complete focus is equivalent to receiving initiation. However, for physical asanas, attending a SKY camp is advised. There is no single "pirate bay" for his works