In Tamil Nadu u can get directly from forest department otherwise contact Institute of Forest Genetics and Tree Breeding (IFGTB) Coimbatore and may be available at TNAU Coimbatore. But sure u can get it from IFGTB. All the best.
Apart from above agencies, you can get seeds from Commercial Seed Traders based in Dehradun, near the FRI campus (location called Panditwari). There is several seed traders, collecting seeds from all states of India in advance with the help their connection with local forest personal. These traders are much more professional than our government agencies.
However, I would like to inform you that you can not get Certified Bamboo seeds from any Govt. or non-Govt agencies in India as unfortunately no agency in India certifying forest seeds with full legal authority unlike several agriculture seeds certifying agencies are doing.