Depends on the spec of your IG coil.
Since you stated that it's a 15 years old car and based on your Location info, your NSX is OBD2 spec.
If my assumption is correct, your IG coil should have 3pin.
For the 3pin style OBD2 misfire detection spec, just get all six (Front x 3, Rear x 3) using the parts no. 06300-PR7-305.
You will get six IG coils at only about US$111 inc. discount and it's not typo.
This price is for all six and not for each coil pack. I think it would be more expensive to buy just a single 3pin coil than buying all six using the above parts no.
For the 2pin style pre-OBD2 spec, I'm afraid there is no such six coil packs deal at great offer from Honda/Acura and you will need to buy it separately or you need to go for the aftermarket one if price is the highest priority.
The failure would most likely to happen at the rear bank if it was related to the rust causing the expansion of the coil head and breaking the wound wire so if you are really keen, you could replace all three at one bank.
However, compared to other popular failure like the Main Relay, IG coil failure is not that common so from this point, you may want to just replace the failed one only.
There are lots of patent involved in IG coil design and misfire detection by each car manufactures so for the IG coil circuit on NSX, you can only check the primary side of the IG coil.
Therefore, unless you have access to the IG coil test rig, you won't be able to check the secondary side with ease and thus, you can only perform partial check on it.
Kaz