Hello Wolfgang,
Now I have to oppose a bit..., sorry please for that.
Matt (merill) is referring to the flat springs in the seat back (Rückenlehne), not the Nosag ones in the seat cushion (Sitzkissen)...
...a few of the flat "springs" are broken...
Well...,
I am not aware of any shop where you could buy these springs 'by the meter'.
This is special steel (spring steel), and always broken in the curves/bends; this is not available.
Specialized seat repair shops can make them by heating, bending and cooling down (hardening).
For my seats I used a specialized shop near Munich;
but I don't have any sources for that stuff separately....
Talk to a few upholstery shops ...
Best,
Achim