Some images from Ian Williams whilst stripping, repairing and recreating a Nippy door lock:
This picture has good detail of the correct bakelite handle:
Ian had contact with Bill Hughes who created the Morgan Series One website here, (see Interior> Door Furniture) and it is likely that the Nippy door catch/locks are the same supplied for the Morgan (below).
Chris Gould has written a Guide to re-making the Nippy door lock using some more available parts where appropriate to do so. Priced £10 including postage from firstname.lastname@example.org.