If you're careful, the rubber gasket on the engine top end cover is very reusable. Just need some high-temp silicone sealant to glue it back down to the lower casing when you're done.
Just in case you still want the gasket info though, here's a
link to a parts fiche with the right part on the page. It's the bottom gasket, Kawasaki part number 11061-0282