a CopySpeed shop nearby? Some of them will print this size for you.
For an image to be of sufficiently high quality for an A3 print you are probably going to have a file size of around 25Mb, so you'll need to find out if they'll print from a CD.
Otherwise, you can send your files to the photgrapher's friends - Digital Labs. What these people don't know about printing from digital files isn't worth knowing, and they'll produce a beautiful print for you. They'll need the files to be properly prepared however, and you can get all the information you need if you