Just to play along...
The facility that created the weapon or weapons would not have to be in Iraq, now would it? We know by looking at his dozens of gold and marble-laiden homes that he had plenty of money to throw around. Cash he would have available to buy, oh, I don't know, weapons. Also, your reactor statement assumes nuclear weapons.
A weapon that can kill 100,000's would fit in the bed of my truck or in any garage or any shack in their country. Not too tough to hide.
Motives, reasons, profits, grudges, and "kick'n his ass for pappa" rhetoric aside, how can anyone argue it was a bad decision to remove him from power? Spend an hour reading what the man did to his people.