visit the NPC that gave you the item and try one of the following key words: "lost", "lost [item name]", "mission" or "quest"
You can try that, and if that doesn't work Black Bert does not sell the Empty Cask you are looking for.
If that doesn't work, unfortunately there is no other way to obtain that item.
You may have to email CIPSOFT, and ask them to help you.
I hope this answers your question.
Cheers!
Jay