Tuning Spring for Gamo Silent Cat Whisper

The wildcat whisper is a nitro piston rifle, not spring.

You'd need to contact Gamo. 

My bad, I read wildcat. 

Yes. Just buy an E3650 from ARH. You’ll need to sand the edges straight. Also maybe ask for him to set the spring or have a spring compressor and some strength ready. Best springs out there too according to consensus. 

Air Rifle Headquarters.... Jim Macarri bought them out some time back. He can probably match your current spring. Other wise remove the old spring and measure the wire diameter, then count the total number of coils, measure the outside dia and the inside dia. Give those dimensions to any of the various spring suppliers and they should be able to match your spring.