GLOBAL CW Locations
 

http://en.wikipedia.org/wiki/Chemical_warfare

Where would this kind of weapons be stockpiled especially in the US?

especially Agent 15 or BZ gas
http://en.wikipedia.org/wiki/3-Quinuclidinyl_benzilate

Some, but remember you have to consider that the munitions at the time of origianal canon were slated to be destroyed in real life. So you can have this stopped or to never have happened and thus stocks of all maner of chemical weapons wuld still be housed.

The problem however is that the munitions still exist but most no longer have launchers in inventory which makes it interesting.

Not only that, but the chemicals themselves lose their potency. That's not to say handling them isn't dangerous, but some types have a 'shelf life' before their battlefield performance begins to downgrade dramatically.

If you burn the refrigerant gas freon you get phosgene as a byproduct. Phosgene was used as a chemical weapon in WWI (military designation CG) and there is no antidote for those exposed to it. Freon would be just as difficult to manufacture post-Twilight War as any other chlorofluorocarbons but existing stocks could conceivably be used to create ad hoc chemical weapons.