The -A version (rather than the vanilla CR-210) has a little mini-tank with circulator pump to avoid the "cold water sandwich" phenomenon, which is the slug of cold water that passes through the tankless before the ignition fires up. If you can plumb around the mini-tank you can probably just toss the pump and it should be fine (unless the controls are too smart, and figure out that the pump is missing. With the tank in the line the cold water sandwich may be exaggerated, since it has to purge the full volume of tepid-tank before the full-temp water would pass.
Have you called Navien America (or the local distributor?) This is a current model, and there SHOULD be parts stock available, but you'd never find the pump from a 3rd party online vendor. (Maybe in Korea you could- do you read Hangul? ;-) )