Look under Crankcase Cover, item #12 COVER, GENERATOR. I have an aftermarket one (chrome, totally looks out of place) after my buddy lowsided the bike. Didnít check flatness of the edge, but gasket paste sealed it up nicely.
I have an NRC cover on mine. Stock are thin enough to get punctured in a driveway drop. I understand that some racing organizations require them, due to the fact that they can lubricate the track in a fall. However, if it's a matter of cost, you might want to check Ebay.