1994 Chevrolet Camaro Z28
Here is another that is never in GTA games from what I have seen. the first version of generation 4 Camaros, the model would be a decent add and the model cost is not outrageous, not sure about the work needed to make it work though.
I actually prefer this this one to the later gen 4 cars but even the later version would be a good add too.
The car model can be found here: