I believe the part number for the nut mentioned in the SB from Lancair should be MS21042-06.  Looks like the typist just dropped the 2.  They are low profile self locking nuts, available from a/s and many other places.  I have a bunch but last time is shipped a half dozen to someone, the package arrived empty.  I had to ship again providing a lot more padding.
BTW I recently received extension buttons from JPI for an EDM800 in a plain white envelope, no note, no protection and no holes in the envelope.  Go Figure.
The photo shown at Aircraft Spruce is an AN963, not an MS21042.  However, the description is correct.
duane es39wg@comcast.net (without posting privileges)