As i can remember in vanilla, the
DM East Black Lotus was in same area than thorium vein at the end of the donjon, and it was always here or quite. As mentionned here :
http://wowwiki.wikia.com/wiki/Black_LotusI remember because when my vanilla time guilds try on Cthun before he was nerfed, that was our only way to have 40 flask / day on the raid to be able to try on him.
If you want to increase the black lotus drop in nostalrius, the easiest way is to add a small chance of dropping a black lotus from random other high level plants.
ie : i gather a dreamfoil and have 1% chance to have a black lotus too.
But you need to fix winter squid first 