Where can I get a spring kit to tune a PGP. My velocity is low and I want to tune it to use constant air form a 13 ci tank. I looked at some springs I had around the house but everything was a bit too big (phantom kit, autococker, spyder springs etc.). I want to do both the valve and main spring. I was thinking I could go to a hardware store and look as well but if there was a kit that would be better. Thanks in advance.