There were two types of replacement-handling units, replacement depots and replacement battalions. Replacement depots were largely static and processed replacements as they were fed through the pipeline to their respective permanent assignments. Replacement battalions were mobile and accompanied assault forces - usually attached to field army- or corps-level commands - as ready pools from which replacements could be drawn as casualties occurred. Don't expect to find a lot of records. Replacement depots and battalions were relatively small, essentially temporary units - permanent personnel constituting the absolute minimum required to process individuals as they passed through. Very often replacements performed certain duties during their relatively brief sojourn.
New Caledonia was just one of many "whistle stops" en route to Japan. If you look at a map, the route from Australia, via Papua, New Guinea, the Philippines, etc. and from Australia, via the Solomons, Gilberts, Marianas, Volcano Islands, etc. form two virtually parallel pathes to Japan. These points along the way were seized or occupied for that very purpose; to form a chain of operating bases that would make possible the ultimate defeat of Japan.