Kerker has quit making exhaust systems for the EX250. Maybe.
They say that if you can't find one on the shelves at a retailer, they'll make one as a special order. Wait time is six weeks. Call them if you're that interested.
As of May, 2006 Bike Bandit was still listing Kerker full exhausts. However, upon calling them, they were unable to confirm whether or not they actually had them in stock. Don't hold your breath.