You should refer to Iravatham Mahadevan's magnum opus. That's the authentic and latest book. It is however, no longer in print. You could possibly loan a copy from state libaries.
Post the publishing of this book, several TB inscriptions have come into light. Most of them have featured in leading newspapers such as "The Hindu". You have to search a lot on the web for that.
In light of the new findingsthe theory of TB script needs a revision and so does the book. I hope and praythe author will be able to publish a second edition of the book.
I wrote on this subject in this forum as an article series. You can refer to that in this group's email archives.