For OEM naca ducts look no further than a 280zx. 79-83. They are functional too. And well made.
I've used those in the past, as well as the 280Z flat hood grill/vent, but they're getting to be harder to find.
T-bird turbo coupe hood vents used to be a favorite of mine as well (used as a scoop on the turbo chicken)
eBay has a whole slew of NACA ducts ( <-link) that could be made to work.
The thing about NACA ducts though, is that they offer no real advantage, that I've read about, as a vent. As a scoop, yes, they can take in air without adding drag, but no real "vacuum" effect as a vent.
BTW - July 22nd is Portland Cars and Coffee JDM day. Not sure, but I might bring the Celica out.
I was thinking something like this near the sides of the hood where water won't dump on anything moisture sensitive
