The standard S3 has smaller discs than the cupra r!
Standard S3 - 315mm x 25mm
Cupra R - 323mm x 28mm
I priced all the parts up at a local Seat dealer first as I was going to go this route but even with discount the price was well over the price of a new Brembo GT kit (£900+)
I managed to find a full Cupra R kit from a local VAG breaker specialist inc discs (only 200miles on them), pads, calipers and caliper carriers.
The calipers were quite scratched from the accident/laying around in the workshop but are in full working order and virtually brand new.....bargain for £400 cheaper than a main dealer!
Just touched the scratches up with a paint stick colour matched from Halfords.