Virtual Ticket selling

I use a paid plugin called License Manager for WooCommerce (found in Themeforest), but also looks like there is a free version.

It can send out random codes, preset imported codes, image based codes that you import, or codes with a prefix or suffix. It does, however, require WooCommerce.

If you had say 20 access codes, you could import them and then sell them, emailed upon completed checkout.