Hi
I would thoroughly recommend that you look up "Sound Affects Premier" in Ormskirk, Lancashire.
From your location, I can see that is some distance - but, if you're interested in 408 guitars, then these really are the guys to talk to.
Not a lot of UK dealers are as passionate about 408s as they are some of the longer-standing products in the PRS catlogue, and that's why they can be difficult to come by. It's a shame, but the reasons for this don't relate to the quality of the guitars. The 408 equipped guitars are outstanding - from the all-mahogany standard models, upwards. I guess that you've realised that already, though
Tim, the proprietor of the store, is an advocate of 408s and that's reflected in the quality and extent of the 408 stock that the store carries. I'm positive that he and his team will be able to assist you in your quest.
I don't have any professional affiliation with them, but lots of good purchasing and px experience.
Great store and a friendly, knowledgeable bunch of guys - and always the best selection of 408 guitars.
Good luck, and do please let me know how you get on (feel free to PM me for any more info, or post below).