This is a relatively simple way to get carbon tetrachloride. Carbon tet is very expensive and difficult to acquire, this is a much cheaper method to get carbon tet. This carbon tet can be purified further with several other purification methods if a higher quality is desired. Large metal extinguishers have a better carbon tet content vs price compared to the pressurized cannister (and smaller metal extinguishers most likely). If the seal is still on you can pretty much know for sure that it hasn't been used and there is still carbon tet in there. You can ask any seller if they hear liquid moving around in it, since it should be pretty obvious. Though for many people the weight can be deceiving and they assume there is something in it while there is not. There are many different brands, while i was searching around i made a list for easier searching since the second hand sites search engines (and people's descriptions) won't show you all of them with 1 search. It also varies by country, USA will probably have more options.

Support my channel:   / chemiolis  

Extinguishers:
Pyrene
Saval
Desmo
QuickAid
ElkHart
Allstate

Cans:
Hero fire extinguisher can (Bostwick Laboratories Inc.)
Fire chief approved extinguisher can (The Fire Chief Co.)
SpeeDee Spray Fire Extinguisher (.... & Dougherty, Inc.)
Allstate fire extinguisher

Other (very expensive for how much it contains):
Red Comet extinguisher
Fire Ball extinguisher
Fire X glass extinguisher
For Fire Shurstop

Refillers (Likely less expensive but very uncommon finds):
Pyrene fire extinguisher liquid
Fyrazer ctc fire extinguisher refill