How to show TV from a coaxial cable on an Apple Thunderbolt Display
You might consider a TV tuner with HDMI output like this:

http://www.newegg.com/Product/Product.aspx?Item=N82E16815260027

Then an HDMI to Display Port or Mini Display Port (Thunderbolt is backwards compatible with Mini Display Port. Display Port would need an adapter to the Mini variety) like this:

http://forums.macrumors.com/showthread.php?t=962633

Shop around for devices such as these. No idea how well any setup would work, I'd love to hear back how well it works out.