There is a backup of the FTP on Archive.org :
https://archive.org/details/ftp.3drealms.com-20090517
All other content on the Downloads page that wasn't on the FTP is listed here, simply copy the links and remove the archive.org part from the URL to reach the link on Fileplanet or wherever it's located:
https://web.archive.org/web/20140208...downloads.html