Exploded view of a GAMO Shadow internals are available in the "Library" section of GTA I believe as well as other places online, however let me ask.... are you positive that the spring is broken ?? There are other things that might prevent your rifle from cocking. Have you taken the rifle apart yet? If you haven't perhaps you should, provided you have a good spring compressor which is a crucial piece of equipment. As for tuning parts...... usually involves deburring metal parts, a new seal, spring, perhaps honing out the piston chamber, application of proper lubes, and a custom made spring guide if you can buy one or have the skills to manufacture one. You can of course just retain and use the stock spring guide if a custom one is not an option for you......
I just checked and the exploded view is in fact available in the "Library",,,, but here's the link anyway............
http://www.gatewaytoairguns.com/library/gamo%20hunter%20220%20through%20890.htmThere's quite a bit of information available on GTA on doing home tunes on GAMO Shadows and other rifles. Take some time, do a search and read the info, I'm sure you'll glean most of the information you will need and what information you don't understand you can always get simply by asking the members
JEff