I have a vintage Purdey, 1888, that needed new springs. The action was sent to Purdey where they farmed the spring work out to another firm. I got it back and it was not right. Back a second time to Purdey where they did get it right themselves.

My point is that this is a very delicate and hard to forge/machine/file part and I would never attempt to make it myself, nor would my Purdey trained gunsmith, here in the US.