Hum, I didn't find any covers with light powered by Kindle but you have these ones.
AYLŪ LED Lighted Kindle Polyurethane Leather Case with Wrist Strap + Screen Protector
AYLŪ Kindle Lighted Crocodile Texture Polyurethane Leather Case + Screen Protector
Just posted them in case someone was searching for a similar effect. If you want them from UK store search for ForeFront.