Cvent has a Marketo connector. Eventbrite will have to be integrated through bedrock or zapier.
We've had this use case too. Eventbrite and Cvent don't really solve this. You need a tool like TimeTrade that ties to Outlook and SFDC. The data can flow into Marketo if you plan it.
We have also used Appointlet, which requires Zapier and isn't ideal.