I would guess, based on your question, that you are thinking about booking a cruise on your own rather than through a travel agent. A travel agent can provide you with a lot of information and save you the time of trying to track down the information yourself. However, you can find out what cabins are available on a given ship, but you need to be diligent, have a lot of patience, and be willing to spend some uninterupted time at your computer. There is no all-purpose web site that lists all available cabins in all categories on all of the cruise ships. What you would need to do is go to the website of the cruise line you're interested in, and look for a heading that says something like "plan my cruise" (or equivalent.) From there, you'll select a destination (Alaska, Caribbean, etc.), number of passengers, length of cruise, which ship, sailing date, etc. You'll probably be given a choice of categories (inside cabin, ocean view, balcony, suite), and be asked which deck. To help with your decision, look for a tab that lets you see the ship's deck plans. Typically, after you've selected the category and deck, cabins that are available will be color-coded in one color (like white), and those that are already booked will be color-coded in a different color (like blue). There are some other steps involved, but I think you get the basic idea. You'll need to go through this procedure for each ship you're interested in. It's not difficult to find what you're looking for, but it is time-consuming. In the same amount of time it would take you to find all of the information you're looking for, an experienced travel agent would get the information for you, brew a pot of coffee, bake a batch of cookies, wash and wax your car, and give you a foot massage! (Travel agents are saying "Yeah.Right.")
there is no one-stop shopping site that has all the unsold cabins of all the cruise lines. I totally agree with the others that a cruise specialist travel agent would be your best bet, otherwise you will have to spend hours on the computer going to each cruiselines web site
Some travel agents get a group of cabins that they can hold for so long and are for sale, but may not show up as booked or not. Best bet, like the previous posters mentioned, get a good agent and they can find out what is available for the dates you want...You may even find one that has some group cabins available and can throw in some extra goodies that you normally would not get, sure worth doing IMHO.
Thanks for your advice. I do have a travel agent that I usually book with, but I enjoy doing my own research to be alert for "fire sale" bargains. I had read that there was information available, though perhaps only to travel agents, as to the number of available cabins by category on future sailings. A large number of unbooked cabins in a particular category after final payment could be an alert to watch for pricing actions by the cruise line on that category on that sailing.
Since we are retired and somewhat flexible, that could be a heads up to check Tuesday specials, etc.