As I was looking for USA to Athens flights on aa.com, I was presented with a MAD connection on April 28. I investigated, and found out that IB has loaded MAD-ATH flights for the following dates only, also listed on iberia.com:
March: 4, 10, 18, 22, 23 (2), 25, 30, 31
April: 28
May: 3, 11, 12
June: 16, 22
Just talked with IB,and they said although the route has been cancelled they will still have some punctual flights (charters, groups, ...) and that you can book them as a "normal passenger" through their website.