AMS has you covered from A to Z. You can get a built long block from them, parts to rebuild the motor yourself, or one of the best KA turbo kits on the market.
IMO, theyre expensive but they have the rep and some badass shop cars to justify their expense. For cheaper/other alternatives, check our list of sponsors. Many of them sell bottom end parts for the KA.
http://www.nicoclub.com/addirectory.shtml
XAT Racing is in Tampa and Enjuku is in Orlando...