Is it a paved road course or a paved oval track?
Most any brand of race kart made in the last 10 years or so can be fairly competitive is usualy prety good quality. Sometimes the frames have been damaged on used karts, so you've got to watch out for that.
Have you found any for sale? Shipping a kart can be expensive so it usualy comes down to whatever used karts you can find within driving distance.
Does your kart race track have a website? If they do, they might have some helpful info and rules posted for the karts your age group races. They might also have a classified section selling used karts all setup to race at that track.