Try the “Search” field above … eg. type “SMP Themes” or “Themes” you will have to spend a few minutes hunting around, but you will find them.
Example: found these that will work on the SMP.
Check out the Live Hub Theme Forum as *most* themes there will work with the SMP (you may have to extract and re-zip the theme to be compatible for upload … but that’s not difficult to do)
In no particular order
http://community.wd.com/t5/WD-TV-Live-Hub-Themes/ALASKA-RESURFACE-REMIX-LIGHT-DARK/td-p/327445
http://community.wd.com/t5/WD-TV-Live-Streaming/Mojo-for-the-SMP-Updated-9-29-12/td-p/287022
http://community.wd.com/t5/WD-TV-Live-Streaming/New-Theme-SENSSIS-WIP/td-p/688813
http://community.wd.com/t5/WD-TV-Live-Hub-Themes/Themes-SteArm-7-WIP2-14th-January/td-p/432898
etc etc … i will let you look for more