The fixed Elnoyle encounter is what I'm assuming you're looking for.
Land the Ragnarok at the Esthar Airstation (looks like a big can sticking out to the immediate west of the Presidential Area on the map.
When you're in Esthar, come towards the screen to exit.
Go south. On the save-point screen, go south. Then go north (along the stairs that have the glowing yellow arrows). And there should be an NPC that looks like an Esthar Soldier, draped completely in black. Talk to him and you'll get an Elnoyle encounter guaranteed.
Leave the screen in any direction (I prefer right, because it's the fastest, imo), return and talk to him again.
Infinite Elnoyle encounters.
--- "Oh no. I knew a guy who leveled up. Ten years later, BAM! Herpes." ~ Vir27 on the importance of Junctioning [FFVIII]