If you know the file is part of a specific public release, search for the CRC or MD5 hash of the pieces you already have to find mirrors that host the complete set. If this is related to something else:
To help you find the exact "piece," please clarify if this is a or a physical object . 1714.rar
Some archives include "Recovery Volumes" ( .rev files). If you have enough of these, you can reconstruct a missing .rar piece using the WinRAR Repair tool. If you know the file is part of