The Collaborative International Dictionary of English v.0.48:

Fashion-monger \Fash"ion-mon`ger\, n.
   One who studies the fashions; a fop; a dandy. --Marston.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fashionmonger
    n 1: someone who advises you about fashionable clothing [syn:
         fashion consultant, fashionmonger]