http://www.scootermercato.com/Scooter-Parts/Gas-Tanks-and-Parts/218585
Not cheap, but I have repaired mine a couple of times;
after squeezing the trapped fuel out, or finding the leak point, I have heated the surrounding plastic area with a solder iron to melt some plastic over the hole. From what I remember, there was a small crack by the seam area of the float.
It has remained leak free for many years since.
I have also used an empty aspirin bottle as a substitute float, but the plastic is not designed to withstand fuel and it falls apart.