Bach provided notes for this publication (5)
I believe the answer is:
'this publication' is the definition.
(organ is a kind of publication)
'bach provided notes' is the wordplay.
I cannot quite see how this works, but
'notes' could be 'ga' (two musical notes) and 'ga' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
Can you help me to learn more?
(Other definitions for organ that I've seen before include "Word after "pipe" or "barrel"" , "notes issue from this" , "Wind instrument found in the body." , "Functional part of body" , "Wind and keyboard instrument" .)