Hello nsayed25
Sorry for the late reply.
Sure, you could also purchase the travel card at Geneva Airport. Any travel center can isse any ticket.
However, I, personally, would not purchase it at Geneva Airport. The staff there is specifically trained for the Geneva’s local public transit network, called Unireso. They might do not know all specifics about the Mobilis fare network of the canton of Vaud. The staff in Lausanne can certainly give better advice on that and knows all the tricks and hacks.
Kind regards,
Roland