Actually they're available at rating 3 (top 50%).
There's also this: https://forums.frontier.co.uk/showthread.php?t=149366&p=2298988&viewfull=1#post2298988
Well that is a new development!! Awesome. But still, joining a faction just to make a ship into a viable explorer seems a little extreme. I'd probably do it though. Do we know for sure that such a fuel scoop even exists?