It never existed. Well, two prototypes were created by a Swedish company Nilsson Special Vehicles AB. They modified two Saab 900s and converted them into longroof models. Only one of them seems to exist today. But just look at what could have been.
I came upon this picture by coincidence. Doing more research on it I was taken to Saabplanet.com. They have a nice story on this and other 900 wagons. Check it out.