What version of X-Plane 11 are you using, as I believe that the rand.bin file is only present from X-Plane 11.30 onwards?
If you have this later version and assuming that you have access to the internet, then the best thing to do is run the X-Plane Installer application, as a part of this process will scan your X-Plane 11 files and replace any that are missing, corrupt or in need of update.
Be aware however, that once you have run the Installer app, your copy of X-Plane 11 will be forever updated to the latest version available, which is currently 11.32. You will not be able to roll it back to an earlier version afterwards, unless you save a copy of your existing version on another disk drive somewhere safe and out of the way!
If you're using the X-Plane 11 DVD set, then run the installer app in the way prescribed for that version.
If you're using X-Plane purchased from any other 3rd party source, then you will have to contact them for advice.