Telephone them. I've found the days that we have wanted available with a phone call direct to Disney when the website shows nothing is available. Some time periods may require starting with less time that you originally want. It is easier to start with nights from Sunday to Thursday night as the weekends book up much faster with Florida residents for just the weekend.
Once you get your 'foot in the door', call back at regular intervals to increase the days until you get what you want.
From middle of Feb, Presidents Day weekend, until April is a very busy time at Disney and Fort Wilderness, but there may be some cancellations from bookings that were made almost a year ago.
Ken