Yes, the ones you can buy from Audi should fit your A3 fine - I bought one for my 1.6 Tdi (single exhaust) and a work colleague fitted 2 to her 1.4tfsi Sport (10 plate). Pretty sure the diameters of the exhaust tips are all the same size.
The one I bought looks identical to the one in Nally's picture. I'll try and dig out the invoice for the part number.
Edit: part number is 8P0071771
i see you can buy the chrome trim to go on them