From what I've seen, those trucks are usually crew trucks for utility companies, railroads, or similar large companies. If you know of any vehicle auctions in your area that may be a place to look.
One guy I met, many years ago, bought what sounds like you are looking for. He knew a salesman that worked at a car dealership that sold a lot of fleet vehicles to the local utility company. They had two vehicles left over from an order (or they had to be repaired, or something), and he got one for a great price. It wasn't overly luxurious, but it had air conditioning!