There used to be a bar weight called the "Bar Snake" that went in the bars instead of using bar-end weights. Don't know if they're still around, though. Some people fill their bars with lead shot. Otherwise, Napoleons act as bar-end weights and are held in place with rubber slugs to further reduce vibes. Also check front end for out of round tire, tire seated properly, stering head bearings adjusted properly, and air pressure. Sometimes it's just a loose nut behind the handlebars.