The most common and most likely answer to this crossword clue is the 5 plus 8 letter word METAL DETECTOR
I've seen this crossword clue in The Daily Telegraph
M
E
T
A
L
D
E
T
E
C
T
O
R
More clues leading to the result METAL DETECTOR
Buddy explains!
The straight part
We know that "Something hard to find? This may help the copper search" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something hard to find? this may help the copper search = metal detector.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.