[RolandF]

Göring came to Fischhorn castle from Obersalzberg via Mauterndorf castle. To both castles he had personal relationships. Mauterndorf finally was too close to the Soviet front so he chose to be taken prisoner by the US.
After being released from Hitler-ordered arrest at Obersalzberg the Siebel probably was requisitioned at Ainring or Maxglan.
P.S.: Different sources claim Göring to have arrived at Fischhorn by car. Maybe some other Luftwaffe highranks being connected with Göring´s surrender left the Siebel standing there, maybe General Koller. The remnants of III./JG 27 spent the last wardays in Saalbach in the Glemm valley, close to Zell am See. Not to mention III./JG 52 at Kaprun.