Serial number 71476 was stamped on October 21, 1938 and cleared final inspection on December 9 that year.
The tuners are Grover G-98 pointed plate tuners with unseamed butterbean buttons.
Style 21 features:
Back and sides: Brazilian rosewood
Top: Red spruce (Adirondack)
Sound hole decoration: Herringbone
Other period features:
Scalloped rear X-bracing
Slotted square fingerboard inlays
Ebony belly bridge
Neck 1-3/4" wide at nut
No C. F. Martin & Co. stamp on back of headstock
C. F. Martin & Co. decal on headstock
At the time of writing (April 12, 2019) this guitar is available at Schoenberg Guitars (http://www.om28.com/ProductDetail?product=P170713002)
Photos courtesy of Schoenberg Guitars.