Unfortunately, it's never been released. It's not unusual for the show's original pilot to not be shown to the public, like the pilot for Gravity Falls, which has only been seen in a clip and a few shots. While we got a few shots from the SVTFOE pilot, the full pilot hasn't appeared anywhere. It'd be cool if it did come out someday, but as of now, it's not available in any way to be watched.
Thanks, I only just found out about the unaired pilot today.
Sorry to add another comment, but two new promos for the show has a few shots that are modified versions of the unaired pilot screenshots. We might not get to see the pilot, but there will be a renovated version of it as a future episode. :)
I really really wanna see the original pilot. :c
and Star-fish Island in it's beta too. ;)