Hal Leonard publishes John Williams (assuming you're talking about the famous film composer, and not the guitarist). If you do a Google search for "John Williams Signature Edition" you should find a bunch of online stores that sell them. Unfortunately they're a bit expensive, which is why I don't have one myself yet...
I think some are original scores, some are transcriptions and arrangements, and some are "orchestral suites." Either way, I imagine they'd get close enough to get the gist of his music.
I think orchestral suites is a good definition for them. I worked for Hal Leonard a while back and did a little work on a few of these titles. These are the orchestrations used in these films, the only difference being is that these are "arranged" for live concert performances. Meaning that the actual cues used in the film didn't always have "endings" and weren't necessarily continous bodies of music. Those types of elements were brought into these scores to create a complete piece of music.
So if you have one of these scores and are listening to a soundtrack recording, the structure might not be identical. But if you're instrested in studying these scores to anaylze his orchestration techniques, then you're looking at exactly what was used in the film.
You might also want to pay attention to the prices: The scores that cost 400ish to 600ish bucks include individual parts for all the orchestra players. The cheaper ones (50-80 USD) are the ones you want.
I know there's a number of places out there that sell legitimate (i.e. royalties paid to the appropriate parties) MIDI files of various songs and compositions. I wonder if there are any out there of his work? If so, they would probably be much less expensive to buy. Admittedly, using your favorite sequencer to print out scores from MIDI will not give you the full features of of the score itself, but it might be an inexpensive way of at least getting familiar with the basics.
Anyone have any recommendations along these lines?