Wow, it must be bad there in UK. Even Amazon is out of Wiis. :O
Meh, I can't really help you. You are the one who knows better your zone.
In my case, I just went to a not-so-famous store, 10 km from here, and their site said they had Wiis. I just went there on the day one at 10am. I just knew no one would go to -that- store to get a Wii. So, I just went there, raced to it and got the only one they had (1 of the 5000 Portugal got for day-one).
So, try to search on less known electronic/domestical shops.
Or, in case you are desperate to play Twilight Princess on Wii (the only thing worth its money), import one from France or Spain or something like that.
Good luck.