Just a point to clear : the 3.7cm Flak 43 boxes and the Flak36/37 ones are different as the clip holds 8 rounds for the Flak43 or 6rounds for the Flak36/37.
I too am seeking for these 8 rounds clips boxes to equip the M÷belwagen...but no avail (unless these are present in the LionRoar/GWM sWS with the 3.7cm Flak ?).
Comparison Flak36 and Flak43 (scroll to the bottom) :http://wehrmachts.kisten.free.fr/rateliers_37mm_2.htm
3.7cm Flak43 :http://wehrmachts.kisten.free.fr/rateliers_3,7cm_2.htm