The problem with RE050A PP sizes is with availability for the NSX front. Most of the most popular and best rear sizes are available, including 225/50-16, 245/40-17, 255/40-17, 255/35-18, and 265/35-18, as well as the oversized 275/35-18. If you want to get a pair of rear RE050A PP to mix with the S-03 on front, feel free; they shouldn't be all that different in terms of handling. The problem will occur when you need to find a matching tire to go on the front.
I am not a dealer. I buy my tires at the usual internet sites - Tire Rack, Discount Tire Direct, etc.