Illegally sells copies, with son in for grand, to no avail (8)
I believe the answer is:
bootless
'to no avail' is the definition.
(bootless can mean useless or without effect)
'illegally sells copies with son' is the wordplay.
'illegally sells copies' becomes 'bootle' (I am not sure about this - if you are sure you should believe this answer much more).
'with' is a charade indicator (letters next to each other).
'son' becomes 'ss' (I've seen this in other clues).
'bootle'+'ss'='BOOTLESS'
'in for grand' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for bootless that I've seen before include "unprofitable" , "unlike puss in Perrault's tale" , "Of little or no use" , "Be so lost (anag) - vain" .)