Since all reservations/staterooms are ultimately controlled and released by DCL, I would guess that only DCL really knows which staterooms are available for a specific cruise date. Since the general public does not have access to the DCL "system," I'd suggest that you contact DCL directly by phone.
You could try to find out "some" availability on your sail date by using the various online reservations services of Dream Unlimited, Expedia, Travelocity and the like.
WebmasterMichelle is right, apparently only DCL knows the complete manifest - the others apparently buy options on blocks of rooms and will not be able to show you the complete picture, just what they have available on their options.
No other choice but ask DCL, for the whole ship on a given date.
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