Yup, 265/35-18 is the most common 18" rear size for the NSX.
Like most brands, Falken makes a lot of different tires - some with great traction, some that last a long time, some that are inexpensive, some whose performance is mediocre. Different tires for different purposes. And other brands make R compound track tires specifically for track use, featuring phenomenal dry traction, as well as generally poor wet traction and short treadlife.
The Falken Azenis RT-615 is about the stickiest street tire available. 265/35-18 is just being introduced now and can be pre-ordered at
Vulcan; the common 215/40-17 front size is already available.
If you're looking for track tires, there are a lot of good ones, although few are available in 215/40-17 and 265/35-18...
What tires do you have in front? Remember, it's a good idea to use the same tires on the front and in the rear, to keep the handling predictable. If you're only buying rear tires, get a pair of the same tires as you already have on the front.