Iraq's chemical weaponry peaked in the 80s, and their supply came from the UK and the USA back when Iran was the big evil and Iraq was the "good guy". Their stockpiles were either degraded or destroyed by the time Gulf War 2 rolled onto the scene. This is why they were never found.

Despite what you might have heard from GIs - Syria has an indigenous chemical weapons program. They secure their precursors and equipment from the international market, and easily circumvented US export controls. Syria has a huge chemical weapons stockpile, but it does not come from Iraq. You can thank the Russians.

Just for some history:

The Baath parties of Iraq and Syria were fierce rivals for the great majority of their mutual existence due to the pivot towards the USSR by Egypt & Syria, and Iraq's alignment with the West and the CIA (whom the Iraqi Baathists owe credit to for their coup). The founder of the Baath movement, a Syrian Christian, actually lived the rest of his life in exile in Iraq.

The truth is always more dull than the conspiracies..