We used this link on two occasions (unfortunately wrote off the first car) and it worked well, we ended up getting exactly this car (A3 S Line 30) from Hereford Audi who were amazing! It did mean two 150 mile journeys though – One to deal with paperwork and one to collect the car.
There are lots in the country although I am unsure of whether you are restricted to the 30 model due to age? (the 30 models are definitely not so easy to find).