Finding used trucks for sale in the region should be straightforward. There are plenty of truck dealers advertising their used trucks here at Truckpages.
An affluent area, the South East covers everywhere south and east of Oxford. Motorway links are good and travel times from other regions are easily manageable.
For export buyers there are six airports serving just the London area alone, so you will have a good choice of locations to fly into. In addition, there is easy access to ports such as Felixstowe and , of course Dover on the South Coast.
There are not too many used trucks for sale in London, as the land is very expensive. You will tend to find the truck dealers and operators on the outskirts of the M25 and beyond.