So I was browsing the Libra Eorzea during some downtime and out of curiosity, I ended up checking the Enemies-tab.
Down there, there are some pretty odd places:
Ragnarok Central Core : T5, area with Twintania & the adds.
Ragnarok Drive Cylinder : T4 mobs
The Ragnarok : I guess T3 mobs

So I though, are we having all the legendary swords (ragnarok, excalibur etc.) as the areas for Binding Coil?