It depends on which resort. The GVs have become increasingly hard to book at 7 months, but then again, Sept and Oct are pretty slow at OKW and probably SSR. September will be easier than October, especially at BWV. Remember, Epcot Food & Wine Fest begins in October, so expect BWV owners to be occupying the GVs there.
So for September, try OKW, BWV or SSR. BWV I expect will be tightest in October, with probably more availability at OKW and SSR then.
Good luck!