I don't know about scooters, but many of the motorcycles I've owned have had a similar condition where the handlebars are slightly out of true with the front wheel. I've tried loosening the bolts that hold the fork tubes and axle, etc and straightened everything and retightened. Sometimes it's helped and somtimes it hasn't. As long as the bike will ride straight while your hands are off the handlebars then it should be okay. If the bike dives to either side when you let go of the handlebars then something is bent. Could be a triple tree or the frame was tweaked in a crash.... could be a lot of things.
I believe the handlebars from the Honda Ruckus are interchangeable with those from the Honda Hullaballoo and the Honda Brouhaha. Not sure if the bars from the Yamaha Riot or Suzuki Pandemonium will work.