There are several 1/18 model's of white 964 911's. The hardest to find is also probably going to be the most expensive. Autoart's Carrera RS. GT Spirit has several 964 911's (Carrera 4 and Turbo that I can think of off hand) available in white as well. They are resin though so there are no opening parts. The other brand I can think of that has a white 964 is Welly (Nex).

While I haven't helped you find exactly what you are looking for, hopefully it will help you get more specific in your search.

Regards,
Robert