The german site BLASTERPARTS sells a lot of Nerf tunung stuff and LARP things.
You also find a Alpha Trooper spring.
http://blasterparts....rf-alphatrooperfor the N-Strike Edition 5kg spring
http://blasterparts....te-alphatrooperfor the N-Strike Elite Edition 7kg spring
This is a modding kit including a 8kg spring, a better catch spring, a guiding shell and bracket
This is a modding kit including a 6-7kg spring, a better catch spring, a guiding shell and bracked
There are moddingkits for every Nerf blaster, except the accustrike and rival, but they will come soon too:)