The Hobbit - Chapter 03 - A Short Rest

[Raynor]

to be quite serious, I really WOULD like the know the story of how those swords came from the fall of Gondolin to hands of the trolls

Well, I for one find Elrond's explanation good enough :

- Whence did the trolls get them, I wonder? said Thorin looking at his sword with new interest.
- I could not say, said Elrond, but one may guess that your trolls had plundered other plunderers, or come on the remnants of old robberies in some hold in the mountains of the North. I have heard that there are still forgotten treasures of old to be found in the deserted caverns of the mines of Moria, since the dwarf and goblin war.