1) Did you put them in your stash after getting them on the character you were playing?
2) Are you using the same username that you got them on, because that makes a big difference.
3) If you somehow lost them to the server, which I doubt, I have a pair I'd be willing to part with.
What you should do is go back to the character you were playing, make sure you put the headphones in your stash, and try to find them on that character. If you can't find them still (make sure you slowly scroll through your stash), let me know either on here or in-game.