Expert Flyer is a big help for this; much faster and eaier to find out which flights have available seats there before you call. So far, it has been 100% accurate for me.
select Aeroflot (SU)
Class(es):
(limit 9) Please first select an Airline.
Business - Award (O)
Economy - Award (X)
Check the boxes for O and X, and then you can play around with days/times/routings before you call DL. Trust me, it's WAYYYY faster.