Tuning parts

hey folks, just joined your forum the nite so sorry if this has already been asked. I recently bought a second hand stealth and am looking to tune it up. i was wandering if internal kits can be bought for these guns like valves, hamers, stems .etc. im looking for anything up to 30-40 ftlbs could any one tell me who or where i could purchase these from if theres such a thing and how much £s. cheers