NY Times article outlining how Assad was able to amass his stockpile of chemical weapons. While the main players appear to be Russia, China, Iran and North Korea, some European countries and the US have also profited from supplying dual use precursor chemicals:

With the World Watching, Syria Amassed Nerve Gas.

Note to Stringsinger, Carroll and the other usual suspects - there is no mention of Israeli complicity but it is the NY Times after all and we all know what that's about, don't we - nudge, nudge, wink, wink.