Thanks for writing in! Regretfully Ethos 3 is part of the standard demo contents. We do not have any links for you to download it. I would recommend that you simply install Ethos 3 demo in your site and replace all the image placeholders by manually downloading the image from the demo site and upload it to your new site. You can then create your slider with a video background and assigned it to the page. If you want to know more about how to use sliders in X, please check this out:
Hope this helps.