You’re probably referring to Salacia oblonga (or S. oblonga) an herb traditionally used in Indian medicine to help control the increase in blood sugar that follows a meal. A study published in the January 2005 issue of the Journal of the American Dietetic Association found that a drink made with the herb blunts this effect and also reduces insulin levels. S. oblonga grows in India and Sri Lanka, but is not well known in the United States, and has not been widely researched.
If you google “diabetes cure” you are directed to websites like WebMD and the Mayo Clinic where you find information on diet, exercise, medication, and insulin therapy, but nothing about the cure. This lack of information may have to do with the fact that Americans spend $322 billion a year to treat diabetes, $60 billion a year on weight-loss programs, and $124 billion a year on snack foods. This is about 3% of the US economy! Because so many peoples’ livelihoods are supported by diabetes and its main cause, obesity, the viral effect of people getting cured and telling others is greatly diminished.