After making an enquiry to Audi UK and as the title suggest I have been able to obtain price and part no. for the exclusive manual gear knob for those S3 owners who may wish to change the OEM.
PART NO. 8V0863278G HVI
PRICE £85.91 plus VAT
The parts can be purchased from the Parts Department and fitted (presumably you can fit it yourself) at your local Audi Centre.