Hi,
I had a pair of spare springs a few years ago made by a chap who used to be on here, I do not recall his full name but I think it was Phil.
These are the measurements of a standard pair as found on my Park RH93 Cal 0.22.
Dimensions and weight of the standard springs:
Short Spring, (pushing front piston rearwards).
3.9mm wire x 19 coils Weight: 108 grammes.
Length: 14.8cm Outside Dia:23.3mm. Internal Dia.:15.5mm.
Long Spring,
3.3mm wire x 29 coils. Weight:94 grammes.
Length: 16.3cm Outside Dia.:18.3mm. Internal Dia.:11.6mm.