Have you considered purchasing one of Thorn's new, ex-display, or used/returned bikes? They are available at a discount over the usual prices. SJS Cycles have a special page listing what's available at:http://www.sjscycles.co.uk/thorn-new-ex-display-used-cycles-and-framesets-dept671_pg1/
Currently offered are a pair
of Ripios, one with sus fork, the other rigid. They're size 595 and claim to fit to 6'2", so might perhaps be close enough depending on how you/they are configured. £1,199.99 for the rigid-fork model. Less robust and therefore unsuitable for your needs but a closer fit is a 610L Mercury; the listing for it states, "...you would need to be 6ft 2"+ to ride this bike".
eBay.co.uk is also a good source. Usual search term is "Thorn bike", though they are sometimes listed otherwise. Some occasionally crop up on our own Forum "Bikes For Sale" listing: http://www.thorncycles.co.uk/forums/index.php?board=16.0
And, of course, we'll keep an eye open for you as well.
Best of luck to you, Darragh; I hope you find your Thorn soon!