LR6 is a standard size 1.5V AA battery available everywhere.
Your local supermarket or corner store will have them.
AA is the size and as far as I can tell LR6 is the Alkaline type.
Sometimes called Penlight or MN1500
http://www.amazon.co.uk/dp/B00SBE7YQ0?psc=1
To the shop with you..., February 2015