Take it to a good auto parts store and see if they have it. I'd call it a rear spindle nut, might help in your search, as you know bearing lock nut is also a good name..
Also look at some 4x4 front spindle nuts, may be some interchange.

With part in hand and if you know the thread size and pitch I expect you have no trouble finding it new

Try this, page 4-67
http://truckhub.us/yahoo_site_admin/assets/docs/Euclid100DWheelAttachingPartsX-Ref.96161249.pdf

Grigg

Last edited by Grigg; 09/11/2013 3:15 PM. Reason: add link
•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-