Why are you thinking that, by restoring a default BGL, you need to reinstall all your addons ?
Just run the Flight sim installer, and choose to "repair" the installation, it will restore only the missing files.
Or, if you don't want to do this, you can simply browse the install DVDs, and look for the file in one of the compressed .CAB files. A compression utility like WinRar will allow you to look inside .CAB files and take files from there.