You shouldn't have a problem seriously
i went to my local Gamestop today to sell some of my GC stuff to get money for the Wii.
I asked him if it would be a problem to get one from here.
"No, you should be able to get on launch day, its basically a first come first serve basis here, but they have 1 million Wii at launch which is basically unheard of for a console. But if you dont get one you wouldn't have to wait much longer till we get another shipment in. You should just keep checking in around launch day to get one, you should be fine"
So seriously, you should be pretty safe from even getting one at EB or Gamestop. I wouldn't reccomend though, i would go with target or something just because they didn't take pre orders. But if i had to say you should be fine on find one on launch day!