Re: first time motorbiker
Welcome to the forum. Sounds as if you're off to a good start. You must have done some reading here and benefited from it.
I'm not sure what you mean when you say your engine came without the ball bearing in the clutch actuating mechanism. If that bearing wasn't there you would not be able to disengage the clutch. Often the bearing is stuck in grease and doesn't come out easily. Are you certain it isn't in there? Whatever, it is 8mm, or 5/16" diameter. It, as well as the steel pin, the bucking bar, that goes in the sprocket/shaft bore needs to be well lubricated with a good grade of bearing grease. The cam in the cover also requires lubrication.
Someone will chime in with a link to a magneto/generator. There is at least one available on ebay but I do not have that link. Some that have used it say it works, some say don't waste your money. You'll have to decide.
Good luck, have fun and ride safe.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"