I've been hearing a lot about people wanting a Ford Crown Vic '90s for GTA IV.
Many modelers said they don't have a model for it.
I have found one:
http://www.3dcadbrowser.com/preview.aspx?modelcode=14916
I don't know if it is useful or not, I just wanted to share it. Many people, including me actually want one in GTA:IV.
Maybe this model is good enough, and someone is cool enough to manage to get it in game.
Hope i've been helpful to some. (: