Stuff on carnatic music is not usually hard to come by. Nowadays, one can look up Arohana/Avarohana of a Raga or list of compositions by a composer with a quick web search. And then there are resources- massive, huge, immense resources- that serious students and researchers should be thankful that they exist online.
Journal of The Music Academy
Madras Music Academy has been publishing this journal since pre-independence era. Many important musicians and musicologists have participated in this. Journal archives from 1929 to 2002 are available online for free.
musicresearch.in hosts some fine scholarly articles, scanned copies of rare books and manuscripts. It’s not a very easy to use site but its contents are invaluable. Recently, they’ve spawned a new site musicresearchlirary.net and are moving rare books and manuscripts there along with some more content.