The index and all the published volumes of the Thesaurus Linguae Latinae (A–M, O–P, and Onomasticon C–D) are now available as open access pdfs from the Bavarian Academy:
http://www.thesaurus.badw.de/tll-digital/tll-open-access.html
Please note that the pdfs may currently be slow to load.
Picture: "Library of the Thesaurus linguae latinae" by N. P. Holmes, licensed under CC BY-SA 3.0