Try this for Maccari springs, etc.http://www.airrifleheadquarters.com/page/page/251327.htm pv
If your spring is not broken and power has not degraded noticeably there is no real advantage to replacing the spring.The amount of twang and torque you experience is related more to how your spring is set up than the brand.Polishing both ends really smooth is key to a lot of twang reduction. I generally use wet or dry sandpaper on a flat submerged in water. I start with 150 grit and proceed from there. If your ends are REALLY bad you may wish to touch them up on a bench grinder first.