Among accessories offered for Mobiky was
this quilted travel bag which should provide better protection than the bag that comes with the bike, but I do not know if it would be adequate for airline travel, or if it is still available.
Larry Lagarde of ridethisbike.com developed
this prototype hard case for the Mobiky in 2006 but apparently did not follow up with it. Then a year later he wrote that he had found
this rolling soft case but did not follow up with that either or reveal the source. These both seem to require removal of the front wheel and handlebar.
You can find more comments about Mobiky from me and other owners by using the "search the forums" feature above.