It's worth mentioning that the reason the NSX does not have the ability to run large lips or really wild concave wheels like what you see on Nissans, BMW's, etc. is due to the double wishbone suspension design placing the brakes far outboard from the centerline of the car. These wheels by contrast run comparatively low offsets for the same widths.
That being said, there are definitely concave wheels available for the NSX.
Here are a couple that come to mind:
Advan RS (we have a set in stock on sale):
http://www.nsxprime.com/forums/showthread.php?t=102516
Volk TE-37 (only available with concave for stock body in 19" rear - we have a demo set in stock for sale at cost):
http://www.scienceofspeed.com/produ...roducts/NSX/Rays/Volk/mono-block/TE37/top.jpg
Work Emotion CR:
http://www.scienceofspeed.com/revolutionized/ScienceofSpeed/NSX/Silver_Turbo/silver_800.jpg
I'm sure others will point out others.
Cheers,
-- Chris