As mentioned before, any springshop/manufacturer can deliver these springs in a wide range of dimensions and materials, my supplier has the cheap ones for just 8 cent a piece and the stainless steel ones (which are better) for about 40 cents a piece. The sad thing is they do come with a minimum outside diameter of 15mm so you have to grind or cut them down to 12mm whis is easy on a lathe.

The set sold by the shop in Germany is also arrounf 14 euro and I think the Xray will not be cheaper.