Akenaton - to manufacture chemical or biological warfare agents is remarkably easy - to "weaponise" them is extremely difficult.

The load that killed all those people in Damascus on the 21st of August will be found to have been delivered courtesy of the Syrian Army/Assad supporters by either a rocket or by artillery shell - indicators of that will be:

1: Dispersal pattern and area covered

2: The fact that it did not linger

Both would be markedly different if either a storage cylinder or a loaded rocket(s) had been hit and had leaked. In the case of the latter the explosion and extreme heat resulting from the detonation of whatever hit the loaded rockets would have destroyed the chemical or biological payload immediately.

US does not have any Sarin weaponry in its arsenal, the USA is however the "site of choice" for many countries for disposal of these agents and most of those agents are transported to the USA for destruction in pressurised storage vessels, not in fused shells or in rocket warheads.