I am looking to paint my radiator shroud due to paint overspray and aging. Is there a paint, flat black or something to keep the natural plastic look.?

Nothing will be "perfect" but good old Krylon Semi Flat will look very nice

or the SEM paint is very good too. Make sure you fog it.

I would recommend using an adhesion promoter after a good cleaning and light scuffing.
Krylon might have a semi-gloss black intended for plastic; I know they have other colors.

I had very good luck using SEM plastic bumper paint. I used in on the plastic shields for the fenders/doors (E-body). They turned out like brand new, and do not look painted at all.
I first glass beaded the parts using a very fine glass bead, then gave them 3 coats. This should work on your rad shroud too.
I also tested this on a junk part first, and the adhesion is very good. I flexed it back and forth many times, and no problems.

Sounds like SEM is the answer, Thanks guys!