I would add that Hackett's online won't ship to the US, nor does the Store Locator list anything in the US. 'Course, finding someone in the UK to act as a proxy for you might well be possible.
Then again, it's really just a slim-fitting blue blazer. It doesn't appear to be unique and remarkable in any obvious way. You could easily buy such a blazer in the US. And again, have white buttons put on it. Just saying, is all. But there's value in being able to try a jacket on before buying it, or to being able to easily return it if it's not quite right.
For that matter, are you even sure the jacket pictured has white buttons? In a photo, metallic buttons reflecting bright light can often appear white. But even if they really are white, swapping out buttons on a jacket is no big deal.