In fact, it's in the IMDb
Since it's a series episode (Season 6, Episode 1), you must go to the series "Family Guy".
"Blue Harvest" is already in our database of existing videos, as you can see by clicking the "existing videos" box of "Family Guy", and going down as it's one of the "various episodes" video (currently $29.49).
So you can add it from there. And even if the video hadn't been in our database of existing videos, you could have added it from scratch.