Most aftermarket upholstery kits are for old Fords or Chevys. Most of those are duplicate of the original upholstery. I don't think there's a market for 99 Sebring seats so they won't be available.
However when I worked for a Chrysler dealer I reupholstered some seats in a car that was vandalized. They got the upholstery from the factory. I don't know how long they stock this stuff but you should check with the parts department at your nearest Chrysler dealer. They might be able to get it in leather.
J.C. Whitney sells vinyl upholstery kits for most cars but not leather.