The Central Institute of Indian Languages (CIIL), Mysore, published a rare 200-page PDF in the 1990s that is still relevant. It uses Tamil script for pronunciation exclusively. Search for "CIIL Chinese Tamil Bilingual Primer."
Most PDF resources available today are designed for beginners. Unlike the saturated market for English-to-Chinese textbooks, Tamil resources are highly focused. Here is what a typical learner will find in these documents: Learn Chinese Through Tamil Pdf
The Chinese Consulate in Chennai has published free booklets titled "Learn Chinese in 30 Days - Tamil Medium." These are often given away at education fairs. Digitized versions float online as PDFs. They focus on tourism and trade vocabulary. The Central Institute of Indian Languages (CIIL), Mysore,