When you right-click the Skins folder, and select Import from the Web, you go to https://creative.adobe.com/addons. Once there, you can type "Robohelp" or "skins" in the search field, and nothing comes up. Not too much luck on Google either.
What did Adobe do with downloadable skins? I'm looking for webhelp non-animated skins, if that helps.
Adobe broke it and doesn't seem interested in putting it back in working order. But hang tight. Hopefully soon you will see them uploaded to the freebies area on the HelpEssentials web site.
If you right-click and select New Skin, pick "Create skin from gallery" then OK, there are a bunch available - not real obvious they exist though.