www.tiresunlimited.com has various tires.
I just bought a supermoto Q-IND set along with a 12-inch rim to upgrade the 10-inch that came stock so I'm now running 12's front and back.
On pavement the Q-IND tires are pretty impressive, very good traction and the bike with 12's feels 100 times better...pretty much feels like a real bike.
Hope this helps!