Ethnic group eccentric’s source of information on course (8)
I believe the answer is:
racecard
'source of information on course' is the definition.
(on a racecourse)
'ethnic group eccentric's' is the wordplay.
'ethnic group' becomes 'race' (a racial group).
'eccentric' becomes 'card' (I've seen this before).
'race'+'card'='RACECARD'
(Other definitions for racecard that I've seen before include "Programme for a horse-meeting" , "List of runners and riders" , "Unscrupulous right-wing politicians may play it" , "Printed details of meeting" .)