Well you don't actually say which side is missing left or right but there are a few part numbers.
Wheel housing liner, plastic left front - 5K0 805 911 E - £21.06 also use 5K0 805 413 see below
Wheel housing liner, plastic right front - 5K0 805 911 D - £21.06
Wheel housing liner, plastic left front - 5K0 805 911 C - £21.06 also use 5K0 805 413 see below
Wheel housing liner, plastic right front - 5K0 805 912 C - £21.06 also use 5K0 805 414 A see below
Wheel housing liner, plastic right front - 5K0 805 912 B - £21.06 also use 5K0 805 414 see below
Oval cover for changing the bulb
Cover wheel housing liner left - 5K0 805 413 - £2.52
Cover wheel housing liner right - 5K0 805 414 A - £2.52
Fixing screws 5x16mm 14 off - N 103 546 02 - £0.25
Speed nuts 5x16mm, 5x11mm 14 off - N 909 591 01 - £0.22