only place I saw one in the UK was here...
Trolling tackle .
Apart from that the US of A seems to have the best selection of drags, But You might just be better buying some metal spoons, crimps, beads and wire from veals or another good UK store and make Your own. I dunno if they have 'self clevis' spoons there but inline spoons will do.
found this whilst looking, might be of interest...
Trolling Spoon