It should work on 5.6. Are you sure you aren't using 5.5 or something else?
Ah, figured it out. The error isn't our server at all:
Source: https://stackoverflow.com/questions/11680709/file-get-contents-give-me-403-forbidden
That particular website has some protection against people using file_get_contents on it. If you use curl with good headers you can get the data from them without them knowing it's not a real browser. That wouldn't stop them from figuring out that the requests are coming from a server not a real persons IP address and if they're really zealous about not having their data scraped they could always block our IP...