These are the parts required for a 312 mm front conversion. The part numbers are Skoda ones because that's what i used:
Left brake caliper housing 1U0 615 123
Right brake caliper housing 1U0 615 124
Brake disc (ventilated) 8N0 615 301 A - Pair
1 set: brake pads with wear indicator for disc brake 1J0 698 151 M
Brake carrier with pad retaining pin 1U0 615 125 - Pair
It is advisable to use the longer Octavia vRS/Audi TT brake hoses when fitting the kit -
Brake hose 1J0 611 701 G - Pair
It is also possible to fit 312mm Brakes to a car that doesn’t have the 288mm brakes as standard but you would require:
Wheel bearing housing left 6Q0 407 255 S
Wheel bearing housing right 6Q0 407 256 S
Wheel hub with bearing 72mm 6Q0 407 621 AJ - Pair
If you want them new it could add up to quite big numbers... aproaching Brembo's Junior kit...