A member on ebay (windycitynsx) was selling the internal marga hills duct, which is somewhat difficult to find... I have purchased from this seller before (seats), and shipping was fast... he has some nice parts (ritmo, marga hills, etc.)
The benefit of these ducts is they're sized to the hood they are intended to go with, so they seal off with the ventilation ducts... if you have a marga hills hood, get a marga hills duct, nsx-r, get a kite garage/downforce/etc. duct, the sos part didn't really fit into a specific category, and has been discontinued since they started carrying downforce products (including their hood duct).
If you have some kind of JGTC hood (louvers) this marga hills (or SOS style) duct might be more beneficial, but not on a nsx-r style hood.