I know this might seem a controversial opinion but ebay is a good place to start. Lots of choice, you can see the feedback history of the seller, and if the car turns out not to be as described, you have easily proved evidence of this in the listing.
I've bought several cars privately over the years using Ebay without any problems at all, then the last car I bought which was coincidentally a 4x4 , we bought from Evan's Halshaw. They were absolutely abysmal.