The 1959 Miller-Meteor Cadilac Ambulance is a very rare and extremely hard to find item. Currently there are none for sale. They are hard to get parts for, and very hard to maintain. There are a few 1961's for sale, check
Ebay.com or one of the many classic car traders. After you invest the maybe up to $30,000 into just getting the restoration done on the car you'll probably need to spend another $1,000-$10,000 on the lights and other stuff. I haven't done any of this myself(yet at least) but if you are really wanting to do this you should ask some of the guys who have done it(they've done AWESOME jobs!)