The scooters are called "Aprilias". From what I understand they actually have a programing component on them that uses a gameboy color cart for speed controlling. All someone had to do was create a rom hack that let you do whatever you want and bam, super fast scooter. The real cart it's self is only given out by aprillia dealers & the like, so it's one of the rarest gameboy color games to my knowledge.
Here's a picture.
http://www.apriliaforum.com/forums/s...d.php?t=158051