This plugin allows you to display/hide download links to certain users who have certain membership level. Requires: S2Member
Just install the plugin and activate it. Then go to Admin > Tools > Orbisius Member Only Downloads. Then click on a theme and the plugin will create a child theme for you.
Go to http://club.orbisius.com and post suggestions in our forum for new features that you'd like to see in this plugin or its extensions.