While the official Montage sounds are proprietary to Yamaha, many independent sound designers create "tribute" or sampled versions. Here are the types of libraries often available:

If the library has a wallpaper and metadata, you can add it to your side panel. If not, simply drag the .nki file directly into the Kontakt window.

Focused on the FM-X engine's crystalline textures.

Always run a virus scan on any "free" executable files. If a download asks you to install a "download manager," it is likely a risk. Stick to direct links or reputable file-sharing sites used by the producer community.