What sort of thing are you looking for? If you would like a shiny Discovery 3 or a Range Rover, most of the main hire companies can provide them. Don't mention the "W" word as most compnaies double the proce as soon as you say "wedding"!
You might fancy something a little different, such as a Land Rover 101, Series I, Tomb Raider, Camel Trophy or G4. In that case, contact the club for that type of vehicle and see if they have any members in your area.