A couple fo things here:
1. Sarin, military grade, IS a WMD. The strength of the Sarin used by Aum Shinrikyo was of poor quality - "homemade" Sarin, if you will. The type of stuff Saddam had stockpiled is "top flight" stuff - binary agents designed to be stored for long periods and remain stable. One drop can kill a person.
2. The artillery shell that was found was unmarked (typical of regimes like Saddam's). It is highly unlikely that the insurgents knew what they had, otherwise they would have used it properly. They thought they were using a fragmentable HE 155mm artillery shell, a nasty thing to be near when they explode.
3. Gas artillery shells, of the type found, are designed to mix the gas after being fired from the artillery piece, then aerosolize on impact. Very little explosive is contained, hence the piss-poor effect as a road side bomb, both from an explosive AND from a gas perspective. As I undertsand it, while the shell was not marked, the bomb squad knew what they were dealing with, and likely took countermeasures (which probably resulted in the accidental detonation - MOP gear is hard to defuse a bomb while wearing)
4. Found one shell.... where there's smoke, there's fire. We didn't find all of Saddam's Air Force yet, either - just a handful of fighters that had become uncovered enough to be distinguished from outcroppings in the desert. Saddam had a LOT of construction projects, and many of them ended with the deaths of the entire crews. He had SECRETS - and 20+ years to prepare to keep them.
5. Actually, a shell with Mustard gas was found on the streets a month or two ago. Little press, because the military downplayed it as an ancient remnant of the Iran-Iraq war. This judgement might have been disinformation, however, to downplay the idea that the "insurgents" might get of looking for more.
6. The search for WMDs will take years. Will they search every crate in every warehouse? How about the potential of desert caches? Can they cross the border into Syria and inspect potential hiding spots Saddam might have been given there? Only an IDIOT would think we should have found "something" by now. Saddam knew EXACTLY what he had and where it was, and it was probably trivial to move and hide then destroy any evidence of such activity. Iraq is a BIG place. 100,000+ troops could maybe form a giant police line - and still only cover 1/100th of the country in a year.
As for who supplied the weapons, it's likely the RAW MATERIALS were supplied by any number of companies from any number of countries. AND? It doesn't require much in the way of controlled materials to build a factory and create chemical weapons (or even biological, for that matter) - it just takes money and infrastructure. It helps to have a cut-throat, ruthless government in place to oversee and prevent leaks. The fact that the shells are unmarked demonstrates that they did NOT come from a NATO or Warsaw Pact country. Most likely, they were manufactured in Iraq.
On a side note, 10 Syrian "technicians" (from Centre d'Etudes et de Recherche Scientific "CERS" - windely seen as Syria's WMD research center) were reportedly killed in that devastating train explosion in North Korea (blamed on Ammonium Nitrate tanker colliding with a fuel tanker - sure - what happened to all the cars that would have been BETWEEN them on the two trains? - "Hey! you got your Ammonium Nitrate in my Petroleum distillate!"). The explosion was akin to a low-yeild nuke, and the NK military dispatched personnel in MOP-type NBC gear - quickly. Some claim it was a tanker of rocket fuel, but again - why would THAT need to be acquired in NK?