ABB make enclosed DC switch disconnectors up to 1000V / 1600A, suited to DC20 duty. If you've got an inductive circuit I think you will struggle to find a switch rated for on-load switching - you may be have more luck looking for a circuit breaker.
Siemens 3WN range of ACB's can switch up to 5000A at 1000V DC, but they are big and expensive. They're available without the overcurrent trip, making them essentially a switch.
Im not sure what you location is thinker but most of the equipment manufactures (sq-D,Siemens,Eaton,G.E.) Can meet your needs I knife blade disconnects and breakers use on 500VDC systems all the time with UPS systems. I do agree a breaker may be a cheaper at the 400amp rating. check with your local electrical parts distributor.
