I downloaded the free photokit try-out and the grain filter hardly produced any.
The good thing about PhotoKit is that it applies layers. You can continue to apply as many as you want and look at the results without actually changing the photo, until you flatten.
Not quite right because black areas have a stipple to them, so I'm still experimenting.
Another idea to try is to take a photo of a white card using grainy film and then scan that and use it as a layer over your photo.
Tina
Tina Manley, ASMP www.tinamanley.com