[Arran]

Judging by the photos what the cabinet originally had was a plain cut French walnut veneer. There are some guys on fleabay that sell it in assorted quantities, lengths and widths, but there are plenty of mail order houses that have it as well including Constantines. It would probably be best to make a straight line patch parallel to the grain where the veneer is chipped out, it's easier then trying to cut and fit a smaller patch to fit the chipped out area and a lot easier then trying to reveneer an entire panel.
Regards
Arran