Avoid random blogspots or file-sharing sites (like Mediafire from unknown users). They often host malware or incomplete copies. Stick to the three sources above.
Ashtanga Sangraha (अष्टाङ्गसंग्रह), authored by Vriddha Vagbhata
around 500 AD, is one of the three foundational texts of Ayurveda known as the Brihatrayi