There's no wine here but you might still find it a source of fun (1,6,2,6)
I believe the answer is:
a barrel of laughs
'there's no wine here but you might still find it a' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'source of fun' is the wordplay.
'source of' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'fun' becomes 'barreloflaughs' (I have seen 'Much fun' mean 'barreloflaughs' so perhaps 'fun' could also mean 'barreloflaughs').
'a'+'barreloflaughs'='A BARREL OF LAUGHS'
Can you help me to learn more?
(Another definition for a barrel of laughs that I've seen is " that's great fun".)