Under "Edit" in the menu bar of some Apps you have an "Undo" option, you could try and see if anything shows in Norton, iTunes or Finder for reversing the trash action.
Failing that you can open the Trash window and select the first item them move to the last and select that while holding the Shift key, that should highlight all the items in between, then drag the selection back out of Trash on to the iTunes open window.
Be aware when you select and manually delete music from iTunes you get a dialogue to delete the reference or delete reference and original file, the former just removes it out of iTunes but leaves the file in it's original location, the latter removes it out of iTunes and trashes the original file, from your description it sounds as though Norton has done the latter but it would be wise to confirm that before dragging them back.