Aldav
All of the big manufactures (GE, Square D, Cutler-Hammer, Siemens, Etc.) make 400 amp combination service entrance devices. You can get them with a single 400 amp breaker feeding the internal 40 circuit loadcenter or with 2-200 amp breakers, 1 feeding the internal loadcenter and the second to feed a remote panel. Square D only make one with the 2-200 amp breakers but I know GE and Cutler-Hammer makes both styles. If you need some part numbers let me know.
Curt
