With regard to the specific question about newer finds of early Brahmi
inscriptions, etc., in southern India, here are some relevant links on
the topic below. I'll look for more later, because I am about to board
an airplane. Here are descriptions and links:

The first link refers to 5th cent BCE Brahmi graffiti from south India,
the second to funerals urns with Brahmi inscriptions from 500 BCE, the
third contains a picture of a Brahmi find, the fouth a book reference
about Brahmi, the fifth a reference to scholar Georg Buhler's dating of
Brahmi to the 8th century BCE, the sixth a reference to potsherds with
Brahmi graffiti from 500 BCE (it includes also links to 1) Palm Leaf
Project and 2) a free Pali-Brahmi Font), the seventh includes refernce
to Tibet's earliest script being based on Brahmi during the 7th century
BCE, but the article is somewhat diffuse. Here they are:

http://en.wikipedia.org/wiki/Tamil-Brahmi
http://varman.org/blog/archives/2006/07/tamilbrahmi_in_thailand.php
http://hindu.com/2006/07/16/stories2006071603952000.htm
http://www.hinduonnet.com/fline/fl2031/stories/20030704000207100.htm
http://answers.yahoo.com/question/index?qid=1006022400523
http://www.nibbanam.com/Brahmi/brahmi.htm
http://www.ibiblio.org/gautam/budd0004.htm