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After digging around Hathi and Google Books I managed to dig up copies of the unique interpolation diagrams ("Diagram A") removed from most volumes of Publication 229 after 1970.  I've put them together into a single PDF for easy reference, along with the versions still published in volumes 5 and 6 for completion's sake, and a copy of diagrams B and C which are common to all volumes.  Don't forget that diagram C should be printed on a transparency.

The scale for the page covering latitudes 15° through 30° isn't quite right.  I'll try to adjust it later.  The distance between the two 30' marks on diagram C should span 8° of latitude along the centerline of diagram A exactly.

Some notes from my staring at these things for way too long:

• The first editions of Pub229 in the US had the seal of the "Department of the Navy Oceanographic Office" on the cover and the title page.  If it has a Department of Defense or NIMA/NGA seal on it, it's a later reprint and won't have the diagrams (except in the high-latitude volumes). 
• Though there's nothing definitive in the text in the books, I think I can infer from the descriptions of the diagrams that they are a "polyconic projection."  Wikipedia calls it an "American Polyconic Projection" specifically.
• The scale along the central meridian is constant (though compressed 1:8 in the diagrams).
• The scale along every curve of latitude is constant
• The latitude curves are arcs of circles, and are not drawn "compressed" like the central meridian is.
• The radius of the latitude circles is a factor of cot(lat), same as in the offset tables in the text (and Bowditch, etc) as well as the curves on diagram B.  The distance from the equator to the unique center of each latitude circle is a factor of csc(lat).
• Within the narrow range of longitude in the diagrams, it looks like all great circles (including the meridians) can be treated as straight lines.