According to "Messerschmitt Me321/323 The Luftwaffe’s “Giants” in World War II, Hans-Peter Dabrowski, [Schiffer, 2002], GS =
Großraumsegler-Staffeln and there were four such units formed at Leipheim & Obertraubling in mid-1941. Each had an authorised strength of 6 x Me321's and several tow-plane flights of Bf110's and He111's. These four GS units were:
GS1 was destined for the Northern sector of the Soviet Union
GS2 was to be the supply & ferry Staffel for all other Großraumsegler-Staffeln
GS22 was to see action in the Central sector of the Soviet Union
GS4 was to see action in the Southern sector of the Soviet Union
With regards GS22, according to page 184 of "Luftwaffe Codes, Markings and Units 1939-45" by B.Rosch [Schiffer, 1995] GS22 was formed in May'41, later to become 3(GS)./KGzbV2 in Mar'42 and then GS-Kdo 1 in Nov'42...
Cheers
Peter D Evans
LEMB Administrator