You can choose to purchase additional event tokens from the Subscription Settings tab of Account Info.
To get there, hover of your name on the top right of your screen and select Account Info from the dropdown.
From there, select the Subscription Settings tab on the left.
Before purchasing your tokens, you can check your Plan Token Usage as well as your Available Event Tokens and Renewal Date
When you are ready to purchase your tokens, click the Buy Additional Event Tokens button.
This will expand a payment window below. Choose the number of tokens you would like to purchase from the dropdown, add your payment information, then click Purchase Token.
That's it! You have now added more event tokens to your account. If you would like to save $200 on every token, consider upgrading your account! More on that here:Upgrade Your Plan