Back in D&D the githyanki had their nice silver swords, and I happened to get one for a character. Now, in Pathfinder, I can't find anything similar. Is there a similar enchantment in Pathfinder? Or did that stay back with the illithids and other proprietary critters?
Nope, no such thing in Pathfinder, at least not AFAIK in the Golarion universe. I don't know if any specific thing has been specified to sever astral cords, but "very few things" implies it's theoretically possible.