For Better BTS AI version 1.01 (BTS 3.19).
A replacement DLL with space for 48 civs. To use, first install the normal Better BTS AI version from here. Then, in the Assets folder, rename or delete the normal Better BTS AI DLL and paste the DLL from this download in its place.
Note that this is definitely not save game compatible with a DLL with any other civ count. In addition, any custom maps or scenarios must have 48 player and team slots defined even if they are empty.