Yes, you can. Enter the text “Gibraltar” only into the search engine and choose the location with the Gibraltar flag. You will see all suppliers both Gibraltar side and Spanish side (La Linea de la Concepcion). ONLY AVIS and BUDGET are located at the terminal of Gibraltar Airport. All the other suppliers are based just across the border (walkable). So if you choose any other suppliers than Avis and Budget your confirmation voucher will provide the precise address in La Linea. Also, for your information, any cars collected at Gibraltar Airport will be Spanish plated and can be driven across the border.