"A forum associated with the site you downloaded the .torrent from is probably the best place to request a reseed. You can also try waiting longer; it's quite possible a seeder has been temporarily knocked offline and will be back in a few days. I wouldn't give up entirely until a week or two have passed.
Finally, you could try to locate other .torrents that include the same file: Load the new torrent in your client but don't let it start a download. Just have it re-check the file you've downloaded. If it's a different version of the file, it won't match your partial download, so you can ignore that and try another .torrent. If it's the same version of the file, it'll match some or all of the partial download, and (assuming this .torrent is seeded) will allow you to complete the download."