The answer is "sorta". I don't think you will find a barrel that will fit in the bottom section of the Weber and still have the lid fit snug. However, what I would suggest is to find a closed top drum that the lid will fit snuggly on. Then cut the drum around one of the ribs where if flares out a bit. Ideally this flared portion should hopefully fit over the lip of the bottom of Weber. Then the lid would fit over the top of the barrel.
Note: the best barrel for this will probably be a closed top drum as they have smaller lips. This will allow the lid to fit without having to pound out the rim of the lid. It might take a little grinding to get it perfect. From there, just cut along the inside of the lip of the drum to open it up. You might try the bottom of the drum as well as those lips are often smaller too.
