I think someone is exagerating something somewhere. There was a 1 or 2 kilogram bottle of potassium cyanide sitting next to me in my lab in grad school. At that time it was pretty easy to get. As Welles says add any strong acid and you get cyanide.
How do you deliver it? It would work well in a subway station perhaps but in open it has all the same problems of mustard gas.
According to Scott Ridder By definition a WMD had to be deliverable over quite a range. Like from one country to another. I dont think cyanide is much good for that without very accurate missiles.
Then again Havana to Miami is not that far, but I suspect this is more propaganda. Cuba does not have the right to make rubber and plastics?