The Delta site typically only shows Z fares for First, and when I called in I was told they can only offer the best fare available (also Z, typically).

However, the site occasionally shows "I" class, for example Jan 1, SFO-LAX has some flights only sold as Z and others only sold as I. Meanwhile, ExpertFlyer shows J9, D9, C9, I9, and Z9 for all flights on that day.

Is there a way to ask to book "I" when only Z is showing on delta.com, but ExpertFlyer shows all F fares as available?