I agree, I have searched high and low....however... i recall a guy in Hong Kong (KS656 or somehing) that did the dual exhaust on his S3. He got hold of a A3 Model and then subsequently modified it to look like his S3. I saw a couple of pictures and he did do a resonable job.
SO if you have the time to do it you can make your own DIY version, you have to get the Audi TT model to nick the wheels off it ans the A4 for the spoiler or something like that. I'll try and find the thread I think it was on TS not on AS though