SVO has the prestige sleeper as well. Last year, IST used to have it too but sadly they have substituted an aircraft with prestige plus now. Actually, for the OP, koreanair.com has a page where you can check which seat is available on which routes on your departure date, but do note that they have been known to change aircraft allocation on a regular basis, sometimes without much warning. Still, even the prestige plus seat is excellent for a lie flat (prestige sleeper is 'very excellent'! ).