Rear springs - alternatives?

[Paxe]

When changing the rear dampers on my -73 P6B I thought I might replace the springs as well. However, it seems as if original ones are hard to get. Does anyone know of alternatives from more modern cars, that you can get at any wellstocked car-mart?

 

[Blueman]

I bought springs, front and rear from a company called Coilsprings and paid totally £145 + (Norwegian) VAT for the springs. They are little lower (25mm) and stiffer than original.
But they also sell standard springs.