Straight from HTC disappeared when they removed the Hub app. Which is probably when that option disappeared. So now you have to resort to 3rd party skins.
Here's a few I just found in the Play Store,
Some are free, some aren't.
I noticed the same thing when I updated to Jellybean. I no longer have the option to "get more" skins. There used to be an option within the skins personalization menu, now u have 5 or 6 skins to choose from and that's it.