Can you call your local police station, and see if they can give you advice? Police departments usually have chemical agents that expire, and they have to get rid of it someplace. I worked in NY State Corrections, and had to be trained in the use of chemical agents, but that was over 15 years ago, and I never bothered to find out what the department did with the CS and CN gas products once they expired.
In my agency it was turned in and disposed of in a central location.
CC
There is no situation that can be improved upon by calling the police.
Those days are long over.
Best just to test it on an unsuspecting welder (worst drivers ever) heh.
He is in Spain.
You would call the Spanish police for advice on what to do with something that is prohibited under Spanish law?