https://www.yamahamusicsoft.com/synths

Pick Motif or MOXF.

If you want free - pick 0-4.99 as the price. Free has a higher probability of having issues. There are more paid ones.

That's one resource.

Here are other places to get content:

If you want to buy Montage performances - there are places to buy those.

https://www.yamahamusicsoft.com/sound-and-expansion-libraries/synth
http://easysounds.eshop.t-online.de/Yamaha-MONTAGE
http://keyboardwaves.com/keyboards-samplers/montage/
Note: not sure above (keyboardwaves) offers performances - description seems to indicate otherwise. Although the Montage version costs slightly more than the Motif XF version - so maybe you get some performances.

Some places do not show Montage targeted sound libraries yet:

http://ksounds.com/yamaha-format-sound-libraries/
http://www.playkeyz.com/
http://www.digitalstudiodesigns.com/
https://www.digitalsoundfactory.com/yamaha_motif_products

If you want to see a collection of Motif-XF only offerings from various library providers:

http://shop.motifator.com/index.php/voice-libraries/motif-xf.html

Copied from another message:

Personally, I think it's jumping the gun to assume all of them work without flaws (would prefer to be able to test them out before listing sources) - but here's a few - there are more:

User submitted work (probably didn't have any compatibility issue in the first place, but now presumably you get the performances too):
https://www.yamahasynth.com/forum/new-collection-of-384-free-voices-for-motif-xf,-motif-xs,-motif-rack-xs-and-yamaha-s90-xs-s70-xs

... actually - no need to reinvent the wheel. This post has a lot already listed with download links. I just checked the first one, some may be "dead":

https://www.yamahasynth.com/forum/yamaha-give-us-more-free-patches-and-soundlibraries-for-the-moxf-thank-you#reply-2940

Copied from the above message (summary):
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Inspiration In A Flash for MOXF: Download
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Inspiration In A Flash + Peter Jungs Symphonic Orchestra for Motif XF*: Write an E-Mail with the subject "MOTIF XF Inspiration & Symphonic" to xfgoodies@easysounds.de
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XSpand Your World, Ethnic, Drumkits, Organs etc. for Motif XS**: Link
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European Loyalty and Oriental for Motif XS**: Write an E-Mail with the subject "MOTIF XS Goodies" to xsgoodies@easysounds.de
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CP1 Piano for Motif XF*: Download
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Peter Jungs VP1 for Motif XF*: Write an E-Mail with the subject "VP1" to vp1@easysounds.de
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Live Hybrid Performer for Motif XF*: Write an E-Mail with the subject "Hybrid" to hybridperformer@easysounds.de
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European Voice Collection for MOXF: Write an E-Mail with the subject "MOXF Free Content" to moxfgoodies@easysounds.de
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Ujiie Voices, EDM Expansion, Twisted Tools Selection etc.: Link
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Free User Library (PSC Songwriters Collection) for MOX/MOXF: Download

NOTE: ABOVE IS A LIST FOR SUMMARY PURPOSES. THAT'S WHY THERE ARE NO LINKS TO CLICK. CLICK ON THE LINK DIRECTLY ABOVE THIS SUMMARY TO BE PRESENTED WITH THE ORIGINAL MESSAGE WHICH DOES HAVE THE LINKS.