The non-profit (archive.org) has preserved countless BlackBerry OS autoloaders. This is currently the safest source for a 9900 autoloader link because the files are scanned for viruses and legally archived.
If you're looking for a specific autoloader link or software package for your BlackBerry 9900, I recommend checking the official BlackBerry website, developer forums, or reputable third-party websites. blackberry 9900 autoloader link