I think white phosphorus manufacturing is pretty open knowledge or atleast the most baic form of manufacturing, its just that its so volatile that generally speaking its not worth it.

Same with nerve agents, ya basically need it on an industrial scale to be effective. Remember that cult in Japan who gassed the subway, they also did the same thing with trucks its just that it diluted and was blown away that only a handful of people died and most got a bad headache at worst.