please take this as the experience of someone who has interacted with TNAU (coimbatore). they are extremely helpful and will assist in anyway possible. yes they are a government organization so you may need to adapt to their work culture. please do not compare corporate processes / work culture with government bodies as it will be alike comparing apples to oranges.
long and short of it, go ahead and meet the TNAU people. if you just call or mail with a casual enquiry it may take awhile for them to respond but they will respond, it is best you go there and meet people. trust me they are pretty serious about what they do. TNAU is a agri university and their experience / consultancy would be a lot cheaper and more reliable than so called 'private consultants'. agree you could always get more specialist consultancy for an area which is extremely good, but at what cost?
improving yield for any crop has no silver bullet formula, you have to take all the options / opinions / technologies etc and decide what is best suited for your requirement/case. i'd suggest the following
1. internet sources (generic / specific by combination of crop, area, soil profile, other factors etc) --> local [tnau, indg, icar, indiaagronet, ikisan, agriculture information, state specific agri department websites] foreign ---> [SARE, ATTRA etc]
2. local kvk's / tnau (for technology, best practices / proven combinations, varieties etc)
3. local farmers (experience , indegenious technologies)