I ordered it from Amazon.de
Its the German version of Amazon and I am British so I can't read it but I got the jist of it anyway because I already have an Amazon.co.uk account. They said they would dispatch a Wii in 4 - 6 weeks. Thats 21st March - 2nd April. It only cost EUR 252.95, that £172, cheaper than in UK shops.
UPDATE : On their website amazon.de it says that they will dispatch the Wii in 5 - 9 weeks! So Amazon have changed my predicted dispatch date to 21st March - 12th April, adding ten days.

blackdamage
But is the WIi that hard to find in UK? I mean, here in Italy you can easily find one in the shelves of some stores.