Look for suppliers of ex-MoD Land Rovers. The armed forces use left-hand drive versions in various countries and they do come up for sale in the UK.
There are some LHD drive Defenders here:
https://secure.pablanchard.co.uk/forsale.asp
Mark, who I've bought from in the past, sometimes has them:
http://www.countyanddefendercentre.co.uk/
The blokes at the Defender Centre, who I've bought from, sometimes have them:
http://www.exmod.co.uk/
Crook Brothers often have LHD ones
http://www.crookbrothers.co.uk/
Also, it's fairly straightforward to convert a soft-top to a pickup. You need the roof, rear window and rear bulkhead from a wrecked pick-up. Defenders are basically giant Meccano sets so you can do this yourself. A look around a few Land Rover forums will turn up people who've done it.
And I did find this very flash one...
http://www.neneoverland.co.uk/4x4leftha ... e04130.htm
But it's the 130 (long wheelbase) and definitely not cheap! Nice, though.
And this company does new LHD ones (for export only) should you ever have the money...
http://www.mod-sales.com/direct/vehicle ... rovers.htm
Hope that helps.