Canine trainer’s source of specialist goods (8)
I believe the answer is:
chandler
'source of specialist goods' is the definition.
(supplier of equipment for boats)
'canine trainer's' is the wordplay.
'canine' becomes 'c' (dental abbreviation).
'trainer' becomes 'handler' (handler is a kind of trainer).
'c'+'handler'='CHANDLER'
(Other definitions for chandler that I've seen before include "Dealer in provisions and supplies,for ships say" , "Dealer in ship's equipment" , "'Raymond ..., US thriller writer (8)'" , "Author of Philip Marlowe thrillers, d.1959" , "Marine items supplier" .)