Get Calypso mixture, boozy in the extreme (4,2)
I believe the answer is:
come by
'get' is the definition.
(coming by is a kind of getting)
'calypso mixture boozy in the extreme' is the wordplay.
'calypso mixture' becomes 'come' (I can't justify this - if you can you should give a lot more credence to this answer).
'in the extreme' means to remove the middle letters (the letters on the extremes of the word are used).
'boozy' with its middle removed is 'by'.
'come'+'by'='COME BY'
Can you help me to learn more?
(Other definitions for come by that I've seen before include "Manage to acquire" , "Manage to obtain" , "Secure" , "Find" , "Encounter" .)