Slyly give rep an unofficial information source (9)
I believe the answer is:
grapevine
'unofficial information source' is the definition.
(as in hearing something on the grapevine)
'slyly give rep an' is the wordplay.
'slyly' is an anagram indicator (I've seen this in other clues).
'give'+'rep'+'an'='giverepan'
'giverepan' with letters rearranged gives 'GRAPEVINE'.
(Other definitions for grapevine that I've seen before include "fruit producer" , "where fruit is grown" , "Bush telegraph" , "Informal channel of information" , "Supposed medium for spreading news" .)