I would hold List<Listing>
at the class level so you can access it when a user clicks on it. I would also throw this on it's own thread and not directly in the Load event. If it's a long process you will hang the ui.
private List<Listing> films { get; set; }
Load
films = LoadListings();
foreach (Listing film in films)
{
cmbMovieListingBox.Items.Add(film.GetFilmTitle());
}
When the user selects the item
Listing film = films.Where(f => f.GetFilmTitle().Equals(cmbMovieListingBox.SelectedValue)).FistOrDefault();
if (film != null)
{
//do work
}