GTS brakes are same as stock, do you mean GR3 / GT5 / GT5-S?
GR4 brakes are Girling or AP Racing, part numbers listed in the homologation papers. Girling are same as used on Lola T70, GT40 a 16/4 and 18/4. You can get reproductions from the UK.
Clutch Master originals unavailable, I know some UK owners get them re-sleeved.
Clutch slave is same as Alfa 105 series https://www.alfaholics.com/par...utch/slave-cylinder/