I didn't see it, but a "cyanide" attack using a chemical weapon would probably be a BLOOD agent (most common is CK) which is perhaps the only such agent that is in fact a gas and lighter than air...quickly disperses and is not persistant. However it is extremely lethal and very rapid in its action...that is from the moment of contamination to the moment of death. Usually this would be delivered by some form of munition...in the case of CK since it is lighter than air...it would seem to preclude an air burst from an artillery shell.
My guess is that the most readily available munition for this agent would be in the form of chemical landmines available by the thousand in poorly guarded warehouses all over the former soviet union. I mean..they had all the real security on the nukes and we know how well those were secured...right?