850 sedan roof spoiler

Roof for a sedan?
Can you post a picture of what you are after?

I'm guessing we're talking about something like this, but I've never seen one in the flesh in Aus.

there a volvo part number for it?

Its this guy with some custom mounting hardware
http://www.volvotips.com/index.php/2012/04/23/painting-the-volvo-v70-rear-roof-spoiler/

IPD have it in stock even...
https://www.ipdusa.com/products/7254/111017-rear-roof-wing-spoiler-for-850-wagon-v70

narly57;91945 wroteLooking for sedan not wagon ............

Volvo never sold one for the sedans
Ever

All the ones you see online are either
1. Custom made
2. From the volvospeed group buy of custom made ones
3. An adaped wagon wing

Thus the above is the one you want and be prepared to have lots of fun fitting it

It's possible the spoiler is from an estate and mounted on the roof of the said sedan.

Yes. Mike said that above.
The dudes on Turbobricks did it that's where the info comes from.

I mounted an 850R wagon spoiler on my T5 April 2017. Love the look it gives to the car. Little mod to the end of the wing to fit the roof and sika flex did the rest. Also had to cut down the roof rail inserts to fit.

The other way is to section the wing in the center but there is a lot that can go wrong with that approach.