I'm thinking it was either recovered during the fall of Thangorodrim and passed to some elf-relative or other of Turgon's, who then got mugged, perhaps in the Misty Mountains, on his way to Rivendell or Lorien some centuries later, or alternatively, it got shipped out before the fall of Beleriand and ended up in Angmar, where it would have made a nice bribe, perhaps to some rather dodgy king of Rhudaur.
I don't buy the idea that a gang of orcs carried it all the way from Beleriand. I mean, OK, nice addition to your basic hoard, but I don't suppose they would have wanted to actually use it or carry it long distances without a good reason, what with its scary anti-goblin glow. Likewise, wouldn't have thought it would be the first thing that a dragon fleeing disaster would have taken. Dragons don't seem to be the kind of creature that would carry baggage long distance.
Hey, here's a thought. I wonder if the Moria Balrog was at the fall of Gondolin, and the sword was something he mislaid in his rush out of Beleriand...? I like that thought. Somehow a Balrog with a backpack sounds more convincing than a dragon.
... also, I wonder if hobbits bred smaller breeds of cow, pigs etc? And were Farmer Maggots big scary dogs actually small terriers?
My icons are not really suitable to this post, but I thought this one could reasonably be described as 'Over the land there lies a long shadow'. :-p