Your password search for 12chan will return better results if you exclude words in your search such as: password, unlock, crack, cracker, remover, hack, extract, open, recovery, winrar, rar, winzip, zip, etc.

You may also search for the URL of where the file that is password protected is located. Most commonly password protected files such as 12chan are downloaded from services such as Rapidshare.com, Megaupload.com, Depositfiles.com, Easy-share.com, Hotfile.com and Uploading.com.

If a file has been downloaded via torrent you may search for the filename of the particular torrent file that is password protected.