ETKA reports that ashtray was only ever fitted to TTs from the factory, both 99-02 and 03-05.
As far as seeing if it "could" fit an an A3, I'd be inclined to say no. Obviously the diagrams in the parts catalogue aren't exactly precise engineering drawings; but they're good enough as a guide; and it looks like they're different enough in dimensions to prevent it...
Regards,
Rob.