Here is a Five second long free Full HD AVI film grain overlay that I made the other day using some real film scans that I am using in my projects.
It is in the Cineform Codec and you need to download the codec for Mac or PC from their website.
Simply drop it into your NLE and use the OVERLAY transfer mode on your track and Voila. Instant film grain.
I will have some 4K versions up soon as well. I have just had a baby daughter so life gets a little busy. Enjoy and let me know if you like them!!!!!