Silver sent abroad for spies (6)
I believe the answer is:
agents
'spies' is the definition.
(I've seen this before)
'silver sent abroad' is the wordplay.
'silver' becomes 'ag' (Ag is the chemical symbol for silver).
'abroad' indicates anagramming the letters.
'sent' is an anagram of 'ents'.
'ag'+'ents'='AGENTS'
'for' is the link.
(Other definitions for agents that I've seen before include "Sales reps" , "They act for others" , "They operate on behalf of others" , "Representatives" , "travelling salesmen" .)