A quick glance (so please verify these part numbers are correct) shows 2 different front springs listed for a GTS, around £150 each + vat
99734353150504 Coil Spring, 1 Set - Identification, Red, Red, Green CARRERA GTS | valid for Special model 911 Carrera GTS (I011) / valid for PASM electronic damper control (I475) | COUPE
99734353149504 Coil Spring, 1 Set - Identification, Silver, Silver CARRERA GTS | valid for Special model 911 Carrera GTS (I011) / valid for Sport-type chassis (I030) | COUPE
and same for rears around £120+ each
1 99733353164504 Coil Spring, 1 Set - Identification, Red, Red, White valid for Special model 911 Carrera GTS (I011) / valid for PASM electronic damper control (I475) | CARRERA GTS
1 99733353173504 Coil Spring, 1 Set - Identification, Silver, Silver, Yellow valid for Special model 911 Carrera GTS (I011) / valid for Sport-type chassis (I030) | CARRERA GTS