The latest word from Capcom is that Street Fighter IV has sold out in Japan. The game was released in Japan on the 12th of February but Capcom has confirmed that "There ARE no more copies to sell on the store shelves."
According to a post on Capcom's blog, "Capcom has a few boxes left in the basement that they'll be sending out on Monday, but they were totally overwhelmed by the demand. Sales couldn't have been any higher because every single day-one copy in the stores was been sold." However, never fear because Capcom has reassured fans that there are more copies in existence.