Dan, how handy with tools are you? Your fix isn't a lighter spring, it's a lighter bolt. You can pick up a replacement bolt from Ebay in the $20 range....and then look it over well. Notice where the bearing surfaces are, the mechanical areas, and the aesthetics areas. Look it over carefully. All the rest can be drilled or dremeled to lighten the bolt. Go small. Metal is easy to remove but harder to put back. Bolt lightening is common in areas where light target ammo is all you can get. Just be aware that that gun was designed to fire "average" ammo in a pretty wide range. Too light and too heavy are the common probs for all semi-auto .22's. So if you mount a lighter bolt, stay away from heavy ammo while you use it!
The prob with lighter springs is as Scoop said. You can use a lighter spring that will allow the light ammo to kick the bolt back, but the light spring will also be light in pushing the bolt back forward into battery. Go lighter bolt, not lighter spring.