It was pretty popular in Japan, and it appears it's doing the same thing here in America.
Capcom's online store is telling those hopeful of ordering Viewtiful Joe some bad news, in big red letters:
Due to overwhelming demand, we are temporarily out of stock for this item. Place your order now to be the first in line for when we have more stock – which will be later this month.
If you can remember, the exact same thing happened in Japan last July when the game shipped out there. This is either a case of Capcom failing to anticipate the demand for VJ, or purposely short-shipping the game to increase it.
Whatever the case, Viewtiful Joe is most likely still available at many other online stores and various retailers around the country. Just because Capcom is (supposedly) out of the game doesn't automatically mean that it will be impossible to find.