Secret stores church found in case, possibly (6)
I believe the answer is:
caches
'secret stores' is the definition.
(I've seen this before)
'church found in case possibly' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'found in' is an insertion indicator.
'possibly' indicates anagramming the letters.
'case' with letters rearranged gives 'caes'.
'ch' put into 'caes' is 'CACHES'.
(Other definitions for caches that I've seen before include "Hidden valuables or ammunition" , "conceal them?" , "Secret stores" , "Secret hoards" .)