First of all, realize the Demo Knife has an extremely fragile backspring. I hear that they break even with normal use. I have one with a broken backspring (a 1978), and finding ones with a broken backspring or two is easy. Plus, a Victorinox Soldier adds an extra screwdriver (that can be used on No. 2 Phillips!) and better awl design. Plus, older ones have the scraper in the bottle opener (1993 and before).
Ontario retired their production of the US Army Utility Knife this year, after they took over from Camillus after they went bankrupt in '08. Those can be found for around $35 new, less than a used Camillus. Vietnam era issuesof the Camillus command a large premium. Imperial made one too for military issue around the same time as Camillus, those are cheaper than the Camillus on the secondary market.
Marbles makes a cheap, Chinese made copy for less than $10. Camillus (the new version who makes all their products in China) makes a repro called the Trench (which is same except for lacking the "US" stamp on the handle and a dated blade, which is around $20
My only guess would be to find some US-based seller who ships to the UK.