Both Revell/Monogram and Airfix have the Saturn V in 1/144 scale and are available almost anywhere. If you want bigger, look on the "bay" for the Revell Sat V in 1/96 scale or the Dragon kit in 1/72, but be prepared to pay scalper's prices for these larger birds.
All of them are able to be built as one or in sections (usually by twist-lock) and ALL of them have published issues or errors. But they are all fixable.
Mike