just a case of pulling everything apart in the house to see what springs are around LOL, you can buy assorted boxes of springs though once you've found your right diameter. I also find simply stretching or cutting a few rings of pending on the effect you want can change the tension to something more suitable or something you like more, i like a firmer spring due to the gun type I use, others may prefer softer..Am surprised most manufacturers dont sell spare springs loaded with different tension for this kind of customization..