Not sure about an NSX, but I removed a power antenna assembly from a Miata and found what's called a sink blank at Lowe's. It's the chrome caps that cover up unused holes in a kitchen sink. They are made out of spring steel, flared at the bottom to hold them in and chrome on top. I just roughed up the chrome with sandpaper, sprayed on primer and then sprayed on touch-up paint to match the car, popped it in and it looks like a factory blank. If you go this route, make sure to get the blank for a stainless steel sink as it will be made to fit thin metal versus a porcelain sink which would rattle around. Also make sure it will actually fit an NSX hole but they sure look the same to me.