Hi Teresa,
Good question. We have two event ticketing plugins, Eventbrite Tickets and WooTickets. They each link our event calendar’s functionality with a pre-existing ticketing system (Eventbrite and WooCommerce).
Both plugins would be able to advertise and sell tickets for a Webinar, my only question on compatibility is dependent on how you plan to control access to the Webinar. If you can tell me a bit more about that, I can hopefully give you some more info. Also, I recommend that you check out the details on both plugins on tri.be and explore the options within Eventbrite as well. That will give you an idea of some of the options out there for managing ticket holders.
Cheers,
Leah