I toured in France back in September and returned to Canada through Charles de Gaulle on Air Canada.
I didn't know about Air France having bike boxes for sale. I visited a few bike shops in Paris and asked for a box. They mostly didn't have any handy in the store, but one guy promised to keep one for me when he built up his next bike.
Of course, that meant I had to take the taxi out to the airport.
One thing to keep in mind: Air France charges 150 euros per flight leg to carry the bike. Air Canada was $50 Canadian. Since the tickets were otherwise the same price, that was the factor that made me go with Air Canada.