Which is the plant of your interest?. You should search in the data base using the botanical genus or family and you will get the isolated compounds related to your plant. Other way is search for anti diabetic plants and will find many species of different botanical family with that pharmacological activity, for example Gentianella Genus.
I think you should look for the database of the location where the herb is found.Or else if the drug is unknown perform simple TLC with mixture of polar and non polar solvents it will give you an idea of the group of metabolites present in the plant.
Most probably according to the habitat the phyto-chemical constituent of the plant varies.So you enter to the collection site of the plant and to the data base of phyto-chemical constituents of anti diabetic plant. Hopefully this will solve your problem to some extent because plants also exhibit systemic variation and seasonal variation.