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 gould323@btinternet.com.
Austin 65/Nippy Archive 
Nice work. Thankfully my old locks and covers are useable, but and I think this is common the actual bit you use to work the lock is often very rusted or lost. Mine has the same steel rod that is reduced to go through the lever arm and is riveted over. I assume there should be some sort of brass or other ferrule over this to actually operate the lock. Does anyone have a picture of the ferrule?
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Although I have not found any undamaged originals to copy I believe the handles Nick refers to were bakelite. Chris Goulds guide suggests a shape and for my replicas I turned some up out of some old bakelite scraps to this design.
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