Is there a legitimate way to get the sword near the middle of the Ancient Maze in Arcanum?

No, there's no way to get the sword. It's a bug or a joke or an oversight, or who knows what, but there is no way to get the sword without editing game files in some way.

Teleportation spells do not work, though in every discussion of the sword that you'll see, there are people who speculate about their use. These people are wrong. There is no way to get the sword.

Anyway, it's just an Arcane Great Sword. Which is nice, but nothing special. There are other ways to get one.