how & where to buy a secondhand car

We are hoping to get a small  run about that we can keep in Italy that will  cope with the strada bianca that have npt been repaired for years. We want a panda 4x4, but not something brand new. We will need a 4x4 and the extra low  first gear would be very useful.We are in Altavaldera, but understand that we may have to go anywhere along the Fi-Pi-Li to  find what we are looking for.We do have residency,  but are not clued up  about the rest of  the process involved in car purchase.Many thanks.