By train: The train from Paris is actually very recommendable. It is comfortable and takes about 4 hours from Paris:
train station Paris Montparnasse - to Rosporden (closest train station to Concarneau) or Quimper.
train station Paris Roissy Charles de Gaulle - Rennes - Rosporden
There are buses between Rosporden (Quimper) and Concarneau
Airport in Paris (Charles de Gaulle CDG or Orly ORY)
please note, the public transportation from Brest airport to Concarneau kind of exists, however, if you are not an adventurer it is not really recommendable.
Please let us know about your travel plans.