Nearby cities of Lorient, Quimper and, more distant Nantes and Brest, have airports. Try to find good connection at www.airfrance.com. Otherwise, take a plane to Paris and a train via Nantes or Rennes to Quimperle or Lorient stations (about 3-5 hours). From both you could be picked-up or could take a taxi to Pont-Aven. Some trains are leaving right from the CDG airport, others - from the Montparnasse station in Paris (use bus connection or RER). Consult train schedule at: www.sncf.com/indexe.htm
More ways: use Ryanair (www.ryanair.com) or other small airlines to Nantes or Brest, then a train.