Here is a link for catalytic converters that are apparently direct bolt on for 1991-1994 NSX's. The price is only $90.60.
http://www.amazon.com/Magnaflow-226...s_2?ie=UTF8&n=15684181&s=automotive&carId=001
http://www.amazon.com/Magnaflow-226...s_2?ie=UTF8&n=15684181&s=automotive&carId=001