Maybe you need one of these? http://www.google.com/products/catalog?q=optical+cable&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&tbm=shop&cid=12430813472282084817&sa=X&ei=ESCDT-XhLIfLgQfRh9X9Bw&ved=0CJsBEPMCMAA
Checking the model and manual for the TV would get you more info as to what you need.
I'd also avoid going to a regular store to buy cables, they are always at a huge markup compared to online shops. Even WalMart.