Robert,
* You may have a null search request as IIRC the magazine acceptance was transitioning to a stick eagle 63 around the "r" block of 1937. By the "u" block, the sE/63 was virtually the only mag acceptance seen. Just make sure a "u" block has the small sE/63 appropriate for 1937 as opposed to the medium or large sE/63 used in 1939.
* The period correct mag should be a blue tube, sheet metal folded/crimped style with the single side pinned alumunum bottom known as the type 2 Mauser military style.
* Trust this helps.