A few of you were asking about these ingame a day or two ago when I said there was a vendor who sold extra ones, like if you wanted to give your companion one too. However when I went looking for him to double check his location he seemed to have disappeared.
He has since returned from his journey and you can find him here;
"My name is Ozymandias, King of Kings:
Look on my works, ye mighty, and despair!"
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare,
The lone and level sands stretch far away.