I am a bit surprised about explanation OP was given. Recently, we decided that we wanted to go MCO-VIE for Christmas in business. It took partner desk about 10 minutes to put together an itinerary. She said that she had to route us MCO-ATL-ORD-CDG-VIE on outbound because seats weren't available via ATL. If reason given to OP was correct, agent wouldn't have been able to do this. Or, is this doable only because we are on AF? If so, OP should be able to fly DL domestic connecting to AF or KLM.

Marc