Yes, the Audi A3 diesel would be a suitable car for long distance drive. The car is comfortable as well as the 2.0 litre engine is well refined. Do remember to take certain pauses during the journey to avoid access heating of the mechanics of the car.
For the availability, we would suggest you walk into the nearest dealership as they will be the better person to assist you because it depends on their stock book. You can click on the following link to see the details of the nearest dealership and selecting your city accordingly - Car Showrooms