Here are som links that could be of use.
https://blog.cognac-expert.com/ (A french site, based in Cognac.)
https://www.just-drinks.com/news/cognac-set-for-future-growth-with-china... (A branch publication on drinks in general, but of course it also contains information about cognac in particular.)
http://www.spiritedsingapore.com/?s=cognac (A Singapore site about alcoholic beverages. Could be interesting as the Asian market is growing?)
http://www.ciedv.org/observatoire.php (A French professional site.)
Also, you could try to contact the French equivalent of Bibblan svarar, they might be able to guide you to more relevant information: http://www.guichetdusavoir.org/index.php?classement=encours
The Swedish school of culinary art in Grythyttan has a library that you could contact: https://www.oru.se/university-library/our-libraries/theschoolofhospitali...