When I have bought Maccari springs they seem to be softer than for example the V-Mach or Vortek offerings. You have to order from the USA but they usually arrive in 7-10 days. I bought one years ago for a BSF55, Maccari believes in 'spacing' springs, so unspaced the spring made about 7 fpe, with some washers to increase the pre-load it made 11.5.
If you send ARH an e-mail I am sure they will advise.
https://www.airrifleheadquarters.com...age/251488.htm