Beyond the official store, a vibrant community has produced a wealth of free and low-cost sound libraries. However, it is important to remember that the Motif XF uses its own proprietary sample format (typically using a flashboard), and these libraries are designed for Kontakt. You would need to own a Motif XF (or a compatible Yamaha synth like the MOXF or Montage) to use them. The table below summarizes some of the most prominent ones.
That being said, there are some websites and forums that offer free sample libraries or cracked versions of software, including Kontakt libraries for the Yamaha Motif XF8. However, I strongly advise against downloading or using such software. yamaha motif xf8 kontakt library free download cracked