This year there are three resorts that will not be available this December that were open last year. Villas at Disney Institute was open last year but it has since closed for conversion into
DVC properties. Also CBR and SoG are currently closed for rehabs. Between the three resorts, that's well over 3,000 rooms that aren't available this year.
On top of that, you have to factor in the way Disney manages their available rooms. Rooms are held in blocks. Imagine a resort has 1000 rooms available. These may be blocked out as 1/3 for Disney, 1/3 for
AAA, and 1/3 for other travel agents. What that means is that CRO/WDTC only has access to booking about 333 of the 1000 rooms. They cannot touch the two blocks of rooms held for AAA and TA's.
Just because CRO has no availability now doesn't mean there won't be later on. At certain pre-defined deadlines, unsold rooms from both AAA and the other travel agents are released back into the system for booking by CRO/WDTC.
Keep calling to add a second room. You should eventually meet with success. Good luck!