It’s probably worth trying a few google image searches - or a few of the many cover sites listed in the Index thread (they often have disc art too).
Could also be an idea to find a Holiday Special image you like - and use that as a template for some disc art.
^ from http://forum.rifftrax.com/index.php?topic=6426.15
Good luck with it - please post up what you do find and use 😃