Where are void container mods located?

I would like to get Shotgun Spaz which is listed on the wiki as being found from a void container. Does this mean it drops from any breakable container within a void mission or from a locker? Also, is there a good place to search for these?

What I've been doing is running various tier exterminate missions and exploring with Master Thief and Thief's Wit mods equipped. I have not found any mods drop from a container or from a locker which drove me to ask. Should I be looking for them in derelicts?