Exclusive stock initially given to supermarket (5)
I believe the answer is:
scoop
'exclusive' is the definition.
(I know that exclusive can be written as scoop)
'stock initially given to supermarket' is the wordplay.
'initially' indicates taking the first letters.
'given to' says to put letters next to each other.
'supermarket' becomes 'Co-op' (The Co-operative).
The initial letter of 'stock' is 's'.
's'+'coop'='SCOOP'
(Other definitions for scoop that I've seen before include "Ice cream serving utensil" , "Hot story" , "exclusively yours?" , "Exclusive report" , "Waugh novel; some ice-cream" .)