When you heat metal it loses some of rigidity, if you cool it fast (use water, cold winter weather, etc.) it will get very hard but somewhat fragile. I guess that this is why nev's springs snapped, they got hardened by too quick cooling.

You can get rigidity back by hammering hot metal, but it changes a bit of other properties.

I had some metalwork lessons in school over 10 years ago, just basics, however I don't know proper english terms

Or you can take the springs to the spring forge and they'll make you new ones with specs you like.. For those who live in Finland:

http://www.vallilantakomo.fi
http://www.pajakulma.fi

They'll also deliver such coil spring as you like. Prices were kinda cheap if I remember correctly. Vallilantakomo also makes sway bars etc... Pajakulma is mainly a heavy duty supplier but they'll also make springs for passenger cars I guess.

I tried to get some information and prices with email from Vallilan Takomo for months ago and still nothing havent heard

Well..maybe i have to call them