I have recently been on the hunt for Wii Fit - it appears to be virtually sold out on-line. Local brick n mortar game stores seem to just receive small quantities every now and then which are quickly snapped up. However I chanced contacting my local Tesco and they happened to have it in stock.
Went down and noticed it was not advertised on the shelves - had to ask at electrical dept. It sounded like they had quite a few in stock.
So if you are after this - it might be worth ringing up your local Tesco to see if they have any as they don't appear to put it out on display (at least in the Bournemouth branch).
Hope that helps!