From what I've experienced recently at work thanks to a fire extinguisher coming loose and smashing into a door at work, a complete door is usually a special order item from the manufacturer.
Are you able to disassemble the door and just replace the pane? Since it's flat glass, making a replacement pane should be fairly simple.
Otherwise have you tried reaching out to a StarTrans dealer? It looks like there's one near Dallas Fort Worth airport, Creative Bus Sales 3880 Valley View Lane Irving, TX 75062.