According the IMDb company credits page: http://www.imdb.com/title/tt1478964/companycredits
The relatively low budget film (8 million pounds) doesn't have a US film distributer yet.
Which doesn't make much sense given the high profile film projects the director, Joe Cornish, is involved with in the immediate future.
Cornish is the writer of the following two films.
(2014) (announced) (screenplay): film to be directed by Edgar Wright.
This writing project is too far ahead and it even might not make it to the production stage.
But the more important one is the VERY HIGHLY anticipated Spielberg directed animated film, The Adventures of Tintin: The Secret of the Unicorn
(2011) (post-production) (screenplay)
Maybe it'll get at least a limited run here in the US. Maybe the distribution companies are waiting to see the box office turnout in the UK before investing any money into the film and allowing the theatrical distribution here.