Most replacement parts from Tikka / Sako older models tend to come in parts "bundles" for example the bolt slide kit for the Sako AV - the only part that ever needs replacing is the small slide guide spring, but you have to get a slide, spring, "cir clip", slide spring guide and another small piece of spring steel which unless you're doing an overhaul are rarely needed.
Consider looking at MSC industrial or Cromwells - they may have springs of the right diameter which you could trim.
I can't advise on tempering and without an electric furness it will be difficult to get to the right temp (although u could wing it with a acetylene torch…)