The DS launched over here in the U.K somewhen in early 2005, however my uncle was going on a business trip to the US in February and he got me one.  If I remember correctly, the DS was sold out at launch but not for long.

Wii on the other hand, was sold out for ages.  I pre-ordered mine at Comet and mine arrived on release on the 8th December 2006.  I took the smart decision to pre-order from a store that isn't normally instantly associated with games and therefore might recieve less interest concerning pre-orders, therefore giving my pre-order a better success rate.

I think that the problem with the wii was that nintendo was not expecting that the sales level will keep strong for so much time , in the first couple of weeks was kind of easy to get one after that was complicated, but with 3DS i think nintendo all ready knows that they will need tons on millions to keep everyone happy , in fact i was concern about this other day cuz i will get a 3DS as soon as it comes out but i live in brazil and will need to import one and this means get one from e-bay or something like that , but i think it will be very easy to get one.