RockAuto are in Madison, Wisconsin, which is a couple of hours from Chicago. The have parts from various manufacturers including NGK who I believe are the OEM supplier to Honda
The list NSX parts under Acura, so you will have to be certain that the part your car requires is exactly the same as the Acura "equivalent", as some parts were upgraded / superseded in different years, and some parts (for example O2 sensors) may have different cable lengths etc.
Another company is Sparkplugs.com, but they are located on the West Coast.
December '99 GH-NA2 110 series - 6AS62 Type S in Monte Carlo Blue Pearl