Thank you for hint, but it's a bit expensive - 10$ for the part... and additionally more than 40$ for the international shipping (I'm not from the US).
I actually gave 120$ for the whole handgun with 2 magazines and this spring is the only issue.
I will manage to make that spring by myself, just need to know the specs. I already made few flat springs for old revolvers and they all work until today (one almost 10 years for now).