It's not very clear from your message, if you don't have parkings at this airport JUST in GSX, or you don't have parkings even when using the standard FSX "Go To Airport" command.
If you have parkings when using the standard FSX "Go To Airport" command, but not in GSX, check the AFCAD being used by GSX, with the "customize airport positions" command, the name will be listed in the top left corner of the window.