That hose is part of the oil cooler piping. No aftermarket option is available so you'll have to get the replacement at a dealership (Nissan part number 21306-JP00A). If you replace the thermostat at the same time and move the coolant reservoir out of the way it should help with gaining access to that end of the hose (...the other end connects by the oil pan). Your radiator hoses look like original equipment--you should consider replacing all of them given what happened.
