Extremely rare, specialist copy (5)
I believe the answer is:
repro
'copy' is the definition.
(I've seen this before)
'extremely rare specialist' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'specialist' becomes 'pro' (professional).
'rare' with its middle taken out is 're'.
're'+'pro'='REPRO'
(Other definitions for repro that I've seen before include "Copying (of a document)" , "Type of furniture" , "Modern copy of period style" , "Copy; copying" , "(Of furniture) a copy" .)