Fairly rare wheels, they pop up from time to time either on ebay or here. I've bought a complete car to get hold of sets before. I've also sold a car with them on as the person was desperate for a set of the wheels or just loved the look of the car with them fitted.
The genuine volvo ones are 17 x 7 inch wide and heres a set on my 740 Turbo.
There is a company in Norway called Eiker that sells Replica Polaris which were slightly wider at 7.5inch wide. They also dont have the outer lip, you can see a set of Eikers on my 740 below. I have yet to see another set of Eikers in this country, many more sets probably exist in europe so widen your search there.
Last time i checked they were around £170 per rim and you'll find there shipping charges are bloody expensive. Cheaper to collect from norway in person or get someone else in Norway to send to you.
In sweden they quite often band the original ones to get an even deeper dish, i've seen them banded out to 11inch wide.