I have just uploaded to the archive.org the three volumes of An alphabetical index of Sanskrit manuscripts in the Government Oriental Manuscripts Library, Madras by S. Kuppuswami Sastri and P. P. Subrahmanya Sastri (1938, 1940, 1942).  See here.

Best,
Dr Dominik Wujastyk
Institut für Südasien-, Tibet- und Buddhismuskunde
Universität Wien
Spitalgasse 2-4, Hof 2, Eingang 2.1
A-1090 Vienna
Austria