In general, RCI only gets spill over inventory from what Vidanta puts in the Registry Collection for the Grand Luxxe units other than the studio/1BR/2BR suite level in resort id # RB71. For the last couple of years it's been limited to the studio and 1 BR loft units in NV tower 5, studio/1BR/2BR villa units in NV, 2 BR spa units in NV and sometimes RM, and Jungle Luxxe 1 BR units in RM. Those are only available for RCI platinum members and the spa and villa units are currently set up so that you can't book through RCI if you own at Vidanta anywhere.
There aren't actually all that many 3 BR units in Interval right now. Vidanta became an affiliated resort for Third Home last year and has been predominantly depositing the 3 BR spa units, 2BR & 3 BR lofts, and 4 BR residence units there instead of in II or Registry. You might see an occasional one in those exchanges because of owner/member deposits, but I don't think too many people do that as there are more cost effective TS to use to exchange in those. They may also be depositing in Elite Alliance, but I never joined that one and don't have access to see what's available there. There are a whole bunch of those units available in Third Home through 2021 right now; resort fee there is $42 per day per unit in both NV and RM.