Hi zebedee and welcom, nice bike you have there.

Not sure a standard exhaust (factory) is going to save you any pennies over an aftermarket one, but you can try Cradley Heath Kawasaki (01384 633455), ask for Road Parts section. They are the largest indepandant Kawasaki parts dealer in the UK and hold a ton of stock, you never know they may have what you want lurking around.