You might try eBay Motors. The 6-volt units are common there, but once in a while a 12-volt motor will show up.

Also, try the LINKS section here at Brickboard. I think they have links to some of the big Volvo mail-order houses. Yes, the motor/fan assemblies are available, but not cheap!

I'm told that a mid-1970's Chevy Blazer fan and blower motor are a drop-in fit, so you might take yours out and carry it around to a few wrecking yards.

On my own PV544, the blower motor never worked since I got the car - not that I'll ever need a heater out here in the desert! I took it apart and it looks as though someone tried to take the fan off the shaft; it's screwed pretty bad.

Not having any wrecking yards to hunt through, I dug out a tubular blower fan from a NASCAR race car, It was used to duct cool air onto the brakes. The intake was 3" and the output was 4", so I just installed it right into the air intake tube that runs from the radiator area up to the heater fan.
Let me see if I can find a picture...



This is the blower I used.



Here, I've painted it black and it's installed into the silver air duct just in front of the original blower.

Not that this will be much use to you...but sometimes if you think 'outside the box' you can come up with an elegant solution!

Steve,
SoCal Desert